Allow Mercurial version numbers with the "rc0", etc., suffixes

[dferreyraosi]

The TortoiseHg About box has started recommending people install what look like release candidate versions; e.g., "tortoisehg-5.9rc0-x64.msi" installs version "5.9rc1":

% hg --version
Mercurial Distributed SCM (version 5.9rc1)
(see https://mercurial-scm.org for more information)

Copyright (C) 2005-2021 Olivia Mackall and others
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.

The trailing "rc1" trips up DoGetVersion().

This commits updates the regular expression to accept these new kinds of version numbers.

[phantomtypist]

I'll have to look into why the build is failing later tonight. Same with the other pull requests you're submitting.