Modified version of Judah's patch

6.6 behaviour:
  - ./.ghci
  - $HOME/.ghci

6.8.[12] behaviour:
  - ./.ghci
  - Windows: c:/Documents and Settings/<user>/.ghci
  - Unix: $HOME/.ghci

6.10 (and 6.8.3 when this is merged):
  - ./.ghci
  - Windows: c:/Documents and Settings/<user>/Application Data/ghc/ghci.conf
  - Unix: $HOME/.ghc/ghci.conf
  - $HOME/.ghci

We will need to document this in the 6.8.3 release notes because it
may affect Windows users who have adapted their setup to 6.8.[12].

Also put the :help docs back within 80 columns

The previous attempt to fix this (#1873, #1360) left a problem that
occurred when the first :load of the program failed (#2049).  

Now I've implemented a different strategy: between :loads, we remember
all the :module commands, and just replay them after a :reload.  This
is in addition to remembering all the package modules added with
:module, which is orthogonal.

This approach is simpler than the previous one, and seems to do the
right thing in all the cases I could think of.  Let's hope this is the
last bug in this series...

When running with ghc -e, exceptions should claim to be from the program
that we are running, not ghc.

You can now give :main a Haskell [String] as an argument, e.g.
:main ["foo", "bar"]
and :run is a variant that takes the name of the function to run.
Also, :main now obeys the -main-is flag.

Patch from Bertram Felgenhauer <int-e@gmx.de>

Readline.initialize spills some escape sequences to stdout for some terminal
types, potentially spoiling  ghc -e  output. So don't initialize readline
unless we're working interactively on a terminal.
Patch from Bertram Felgenhauer <int-e@gmx.de>

Teach GHCi to show a "perhaps you forgot to use :trace?" when
it finds that the user is trying to retrieve an empty :history

Seems better than getting a confusing 'cannot find directory' exception.

Ian Lynagh <igloo@earth.li>**20071124231857
 It used to be a synonym for ":r" in 6.6.1, but this wasn't documented or
 known about by the developers. In 6.8.1 it was accidentally broken.
 This patch brings it back, but as "repeat the last command", similar to
 pressing enter in gdb. This is almost as good for people who want it to
 reload, and means that it can also be used to repeat commands like :step.

- add example to docs, explain how to interpret 
  output of `:browse! Data.Maybe`
- print unqualified names according to current 
  context, not the context of the target module

I think I figured out a reasonable way to manage the GHCi context,
comments welcome.

Rule 1: external package modules in the context are persistent.  That
is, when you say 'import Data.Maybe' it survives over :load, :add,
:reload and :cd.

Rule 2: :load and :add remove all home-package modules from the
context and add the rightmost target, as a *-module if possible.  This
is as before, and makes sense for :load because we're starting a new
program; the old home-package modules don't make sense any more.  For
:add, it usually does what you want, because the new target will
become the context.

Rule 3: any modules from the context that fail to load during a
:reload are remembered, and re-added to the context at the next
successful :reload.

Claus' suggestion about adding the "remembered" modules to the prompt
prefixed with a ! is implemented but commented out.  I couldn't
decide whether it was useful or confusing.

One difference that people might notice is that after a :reload where
there were errors, GHCi would previously dump you in the most recent
module that it loaded.  Now it dumps you in whatever subset of the
current context still makes sense, and in the common case that will
probably be {Prelude}.

GHCi input is now treated universally as UTF-8, except for the Windows
console where we do the correct conversion from the current code
page (see System.Win32.stringToUnicode).

That leaves non-UTF-8 locales on Unix as unsupported, but (a) we only
accept source files in UTF-8 anyway, and (b) UTF-8 is quite ubiquitous
as the default locale.

The contents of bindings show at breakpoints and by :show bindings
is rendered using the same printer that :print uses.
But sometimes the output it gives spans over too many lines and the
user may want to be able to disable it.

Sorry, should have pushed with previous batch of changes.

- :def! now overwrites a previous command with the same name
- :def on its own lists the defined macros
- ":undef f g" undefines both f and g

   
  - :browse!
    a variant of :browse that lists children separately,
    not in context, and gives import qualifiers in comments

SimonM: I also added sorting by source location for interpreted
modules in :browse, and alphabetic sorting by name otherwise.  For
:browse *M, the locally-defined names come before the external ones.

  - :{ ..lines.. :} (multiline commands)
    allow existing commands to be spread over multiple lines
    to improve readability, both interactively and in .ghci
    (includes a refactoring that unifies the previous three
    command loops into one, runCommands, fed from cmdqueue,
    file, or readline)

  - :set
      now shows GHCi-specific flag settings (printing/
      debugger), as well as non-language dynamic flag 
      settings
    :show languages
      show active language flags
    :show packages
      show active package flags as well as implicitly 
      loaded packages

This required moving PackageId from PackageConfig to Module