util: move checklink() to posix.py and return False on Windows
Python added support for Windows 6.0 (Vista) symbolic links in 3.2 [1], but
even these symbolic links aren't what we can expect from a canonical
symbolic link, since creation requires SeCreateSymbolicLinkPrivilege,
which typically only admins have.
So we can safely assume that we don't have symbolic links on Windows.
[1] http://docs.python.org/py3k/library/os.html#os.symlink
util: make 'hg log -d --2' abort (
issue2734)
help: sort help topics to make the output more readable (
issue2751)