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Should fix an occasional build error of the form 
 ghc-pkg: too few bytes. Failed reading at byte position 8

So ghc-pkg register/update takes input in UTF-8, and ghc-pkg dump
outputs in UTF-8.  Textual package config files in the package DB are
assumed to be in UTF-8.

 - the package DB is a directory containing one file per package
   instance (#723)

 - there is a binary cache of the database (#593, #2089)

 - the binary package is now a boot package

 - there is a new package, bin-package-db, containing the Binary
   instance of InstalledPackageInfo for the binary cache.

Also included in this patch

 - Use colour in 'ghc-pkg list' to indicate broken or hidden packages
  
   Broken packages are red, hidden packages are 
  
   Colour support comes from the terminfo package, and is only used when
    - not --simple-output
    - stdout is a TTY
    - the terminal type has colour capability

 - Fix the bug that 'ghc-pkg list --user' shows everything as broken

See commentary at
http://hackage.haskell.org/trac/ghc/wiki/Commentary/Packages

We now look for missing files (including .hi files), and report all
the packages that are transitively broken.

$ ghc-pkg check 
There are problems in package syb-0.1.0.0:
  dependency foo-4.0.0.0 doesn't exist
There are problems in package process-1.0.1.1:
  file System/Process.hi is missing

The following packages are broken, either because they have a problem
listed above, or because they depend on a broken package.
syb-0.1.0.0
process-1.0.1.1
base-3.0.3.0
Cabal-1.7.0
haskell98-1.0.1.0
haddock-2.4.2
ghc-6.11

We allowed non-existence before because the user DB is allowed to not
exist, so now we have an explicit exception for that case.

It was calling openTempFile which uses a 600 permissions mask.

This was broken in the System.FilePath switchover, since filepath's
splitSearchPath doesn't do what we want (it ignores empty
components on Windows, and treats them as "." on Unix).  So we use our
own hand-rolled version, just like GHC.

This depends on #2298 also being fixed, which I'll do shortly