This patch fixes a couple of issues with the
    Be lazier in user config creation, and don't fail on missing configs.
patch. It puts the createDirectoryIfMissing back in and removes assumptions
that the package.conf file already exists.

Consistently used spaces rather than tabs.
Removed trailing whitespace.
Wrapped comments to fit in a standard terminal.

	MERGE TO STABLE

Fixes Trac #827
Test is should_compiler/ds058

  This allows you to put -fcontext-stack into an options pragma,
  as requested by Trac #829
  
  While I was at it, I added OptIntPrefix to the forms allowed
  in CmdLineParser.

I measured that this makes the comiler allocate a bit more, but it
might also make it faster and reduce residency.  The extra allocation
is probably just because we're not inlining enough somewhere, so I
think this change is a step in the right direction.

It turned out that newUnique was wasting one node of the splittable
uniq supply per invocation: it took the current supply, split it, used
the unique from one half and stored the other half in the monad.  In
other words, the unique in the supply stored in the monad was never
used.  

This optimisation fixes that and adds a bit of strictness, which
together lead to small reduction in allocations by the compiler, and
possibly an improvement in residency (hard to tell for sure when GCs
move around).

The I# constructor is always removed when we make a unique later
anyway, so this just saves a bit of time and allocation.

Now that the module restriction has been lifted, the auto-hiding is
mostly not required.  GHC itself automatically hides old versions of a
package.

This patch pushes through one fundamental change: a module is now
identified by the pair of its package and module name, whereas
previously it was identified by its module name alone.  This means
that now a program can contain multiple modules with the same name, as
long as they belong to different packages.

This is a language change - the Haskell report says nothing about
packages, but it is now necessary to understand packages in order to
understand GHC's module system.  For example, a type T from module M
in package P is different from a type T from module M in package Q.
Previously this wasn't an issue because there could only be a single
module M in the program.

The "module restriction" on combining packages has therefore been
lifted, and a program can contain multiple versions of the same
package.

Note that none of the proposed syntax changes have yet been
implemented, but the architecture is geared towards supporting import
declarations qualified by package name, and that is probably the next
step.

It is now necessary to specify the package name when compiling a
package, using the -package-name flag (which has been un-deprecated).
Fortunately Cabal still uses -package-name.

Certain packages are "wired in".  Currently the wired-in packages are:
base, haskell98, template-haskell and rts, and are always referred to
by these versionless names.  Other packages are referred to with full
package IDs (eg. "network-1.0").  This is because the compiler needs
to refer to entities in the wired-in packages, and we didn't want to
bake the version of these packages into the comiler.  It's conceivable
that someone might want to upgrade the base package independently of
GHC.

Internal changes:

  - There are two module-related types:

        ModuleName      just a FastString, the name of a module
        Module          a pair of a PackageId and ModuleName

    A mapping from ModuleName can be a UniqFM, but a mapping from Module
    must be a FiniteMap (we provide it as ModuleEnv).

  - The "HomeModules" type that was passed around the compiler is now
    gone, replaced in most cases by the current package name which is
    contained in DynFlags.  We can tell whether a Module comes from the
    current package by comparing its package name against the current
    package.

  - While I was here, I changed PrintUnqual to be a little more useful:
    it now returns the ModuleName that the identifier should be qualified
    with according to the current scope, rather than its original
    module.  Also, PrintUnqual tells whether to qualify module names with
    package names (currently unused).

Docs to follow.

In all cases the namespace is known from the context, so this saves 1
byte per variable binding/occurrence (a few percent per iface file).