zsh completion: add subrepos options for all supporting commands

zsh completion: add new option groups for options Add clone, date/user, git-style, merge tool, ignore space, log, branch/bookmarks options and use them throughout command completions.

zsh completion: add `forget` and `rollback` commands

zsh completion: complete additional topics for `help`, not commands only

Merge with stable

tests: merging bookmarked heads 45b5eb2941d0 fixed an error that occured when heads being merged were both inactive bookmarks. Add a test for that case.

merge with stable

debuginstall: show directory for Python lib Example new output on Windows: $ hg debuginstall checking encoding (cp1252)... checking Python lib (C:\Users\adi\hgrepos\hg-main\hg-python\lib)... checking installed modules (C:\Users\adi\hgrepos\hg-main\mercurial)... checking templates (C:\Users\adi\hgrepos\hg-main\mercurial\templates)... checking commit editor... C:\Program Files (x86)\Notepad++\notepad++.exe checking username... no problems detected on Linux: adi@kork-ubuntu64:~/hgrepos/hg-main$ ./hg debuginstall checking encoding (UTF-8)... checking Python lib (/usr/lib/python2.7)... checking installed modules (/home/adi/hgrepos/hg-main/mercurial)... checking templates (/home/adi/hgrepos/hg-main/mercurial/templates)... checking commit editor... checking username... no problems detected

util: replace util.nulldev with os.devnull Python since 2.4 has supported os.devnull so having util.nulldev is unnecessary.

revset: add hidden() revset

wix: bump MSI based installers to use Python 2.7 We're somewhat forced to use Python 2.7 for the bdist packages, so we might as well use 2.7 for the MSI installers as well.

merge with stable

tests: fix template test output

merge: handle case when heads are all bookmarks If all heads are bookmarks, merge fails to find what node to merge with (throws an IndexError while indexing into the non-bookmark heads list) as of 4a02cf4fbb2e. This catches that case and prints an error to specify a rev explicitly.