Add showSimpleInstalledPackageInfoField

This is like showInstalledPackageInfoField, but uses a simpler output
form. Used by ghc-pkg for its --simple-output mode.
Merge branch 'master' of github.com:haskell/cabal
Explain why we use > instead for >= for modification time checks.
Don't forget to close the 'index-00.tar' handle.
Use 'notice' instead of 'info'.
Revert the old behaviour of listBuildTreeRefs.

Also make it possible to list ignored build tree refs (those present in the
index file but not in the source package DB).
Gently point the user in the direction of 'sandbox delete-source'.

We don't show that command in 'sandbox help' output by default, but if the user
is running 'list-sources', she probably wants to know about it.
Merge pull request #1300 from 23Skidoo/misc-fixes

Misc fixes here and there