Code review comment for lp:~doxxx/bzr/cmdline-splitter

At John's suggestion, I've reworked my fix for bug 392428 to entirely replace bzr's use of the shlex module with a commandline splitter that works for all platforms. This resides in a new module called bzrlib.cmdline which provides a Splitter class for complete control over how splitting is done and a split() helper function, which defaults to supporting single quotes.

bzrlib.commands.shlex_split_unicode() has been removed in favour of bzrlib.cmdline.split().

Processing of the win32 bzr commandline allows single quotes for quoting arguments. I can revert that, if desired, without affecting single quote support in aliases, etc.

I've tested this with selftest on Windows 7 and Debian.