bdiff.c: Added support for py3k.
This patch adds support for py3k in bdiff.c. This is accomplished by including
a header file responsible for abstracting the API differences between python 2
and python 3.
% before commit
% store can be written by the group, other files cannot
% store is setgid
00700 ./.hg/
00600 ./.hg/00changelog.i
00600 ./.hg/requires
00770 ./.hg/store/
% after commit
% working dir files can only be written by the owner
% files created in .hg can be written by the group
% (in particular, store/**, dirstate, branch cache file, undo files)
% new directories are setgid
00700 ./.hg/
00600 ./.hg/00changelog.i
00660 ./.hg/dirstate
00660 ./.hg/last-message.txt
00600 ./.hg/requires
00770 ./.hg/store/
00660 ./.hg/store/00changelog.i
00660 ./.hg/store/00manifest.i
00770 ./.hg/store/data/
00770 ./.hg/store/data/dir/
00660 ./.hg/store/data/dir/bar.i
00660 ./.hg/store/data/foo.i
00660 ./.hg/store/fncache
00660 ./.hg/store/undo
00660 ./.hg/undo.branch
00660 ./.hg/undo.desc
00660 ./.hg/undo.dirstate
00700 ./dir/
00600 ./dir/bar
00600 ./foo
% before push
% group can write everything
00770 ../push/.hg/
00660 ../push/.hg/00changelog.i
00660 ../push/.hg/requires
00770 ../push/.hg/store/
% after push
% group can still write everything
00770 ../push/.hg/
00660 ../push/.hg/00changelog.i
00660 ../push/.hg/branchheads.cache
00660 ../push/.hg/requires
00770 ../push/.hg/store/
00660 ../push/.hg/store/00changelog.i
00660 ../push/.hg/store/00manifest.i
00770 ../push/.hg/store/data/
00770 ../push/.hg/store/data/dir/
00660 ../push/.hg/store/data/dir/bar.i
00660 ../push/.hg/store/data/foo.i
00660 ../push/.hg/store/fncache
00660 ../push/.hg/store/undo
00660 ../push/.hg/undo.branch
00660 ../push/.hg/undo.desc
00660 ../push/.hg/undo.dirstate