Do not use static-libgcc flag on Darwin
ncurses: apply a patch on Darwin for a clang bug
proofgeneral_4_3_pre: Add expression needed for current prooftree
proofgeneral: Delete default.nix for proofgeneral
retroshare: place plugins at proper place

Now they can be used.
Merge pull request #2983 from jwiegley/zlib

Do not use static-libgcc flag on Darwin
Merge pull request #2986 from jwiegley/ncurses

ncurses: apply a patch on Darwin for a clang bug
git-annex: Build on Darwin, let Cabal determine proper flags
Merge pull request #3031 from jwiegley/proofgeneral

proofgeneral_4_3_pre: Add expression needed for current prooftree
Merge remote-tracking branch 'upstream/master'