This is needed to separate Cabal and subprogram output if stdout is
buffered (e.g. a file), especially if stdout and stderr are the same.

Fixes ticket #11. Though the section could do with a bit more detail.
It corresponds to what's on the wiki:
http://hackage.haskell.org/trac/hackage/wiki/StableInterfaces

The System.IO.openTempFile is much better because it opens the temp files
securely. Howver it is only available in base-2 and only of GHC. In base-3
it is available for all implementations. So in practice that means it's only
for GHC and we have to use our compatability implementation for hugs and
nhc98. Not sure of the status for jhc.

ghc-6.4 and above recognise the OPTIONS_GHC pragma.
ghc-6.6 and above recognise the LANGUAGE pragma.
Added OPTIONS_JHC and OPTIONS_NHC pragmas with equivalant flags.

Dissalows version strings like "1.05". It'd have to be "1.5" or "1.0.5".
That is, leading '0's in version components are no longer allowed.
The Version parser & pretty printer should now be exactly 1-1 and invertable.

Previusly everyone got the compat version, except for ghc and hugs which
opted out. Now just nhc98 opts in.

No longer inlcude compatability hacks and remove code that handles
the old style of ghc-pkg package registration files.

setup configure takes a --with-compiler option, but used to change 
that into a --with-hc option when calling ./configure.
Now that we've added autoconfUserHooks and deprecated defaultUserHooks we
can fix this without breaking any existing scripts. The autoconfUserHooks
now passes --with-compiler to ./configure and defaultUserHooks is unchanged.
Fixes ticket #114.

Setup scripts should switch to simpleUserHooks or autoconfUserHooks.
autoconfUserHooks now fails if ./configure is not present.
defaultUserHooks does the same thing it always did.

since you can get the same effect just by setting the command's default flags
to empty.

Also extend the check. It's now a QA error to use a license that is empty
or AllRightsReserved. It's a warning to not specify a license file. It's an
error for the license file to be given but not exist.
Note that QA errors are not fatal for generating tarballs. But they will become
fatal errors for uploading to the public hackage server. It will still be
possible to use AllRightsReserved or another license on a private hackagedb.

Code written in a session with Duncan Coutts

Much code written in a session with Duncan Coutts

Addresses #191 (QA) and #180 (QA for missing license).
This patch only adds a new exposed module, it's not yet used anywhere.

So they should be safe to remove now.

Fixed:
http://hackage.haskell.org/trac/hackage/ticket/176

because we use the value of configUserInstall to set the default value for
configPackageDB, and any value the user sets will override that.