misc: update descriptions about removed file for filectxfn Since 650b5b6e75ed, filectxfn for memctx should return None for removed file instead of raising IOError.

osx: always purge build/mercurial before starting build This prevents stray files from previous builds from polluting newer builds.

osx: use more paranoid quoting in test

osx: install completion scripts using install(1) to avoid umask badness This actually fixes some tests that were showing us umask badness that had been overlooked.

merge with stable

py3: prove `hg {add,addremove,commit} all work We can't do a second commit in a repo yet, because pure-Python bdiff is broken on Python 3. That is probably a good next step.