ghc-7.6.3: undo commit 7c8ba75

The change was supposed to trigger a re-build to fix a broken GHC binary
on the Hydra build farm, but now it turns out that the cause for the
errors we're seeing isn't GHC: all kinds of (non-Haskell) packages are
broken.
gnum4: update to version 1.4.17
gnum4: fix download URL
gnum4: drop obsolete patches
Merge remote-tracking branch 'official/stdenv-updates' into stdenv-updates

Conflicts:
	pkgs/development/compilers/ghc/7.6.3.nix
Revert "gfortran: update to 4.8.1"

This reverts commit c3edfa427e7ae0efca7a2843a2ebc0dad5a23484.