Got MSVC 2010 working (but in a hacky way).

Borrowed code from Cardiac Atlas Project buildbot (not sure if it was written by them or borrowed from elsewhere).
Notes:
1) Other ABI buildbot configs at ABI take a different approach to variations between configs.
The approach taken here is a bit of a hack, just to get things working. It may be OK, since currently
the family of slaves are all the same except for the one MSVC 2010, so the more generic approach may be overkill.
2) An upgrade to the build master would mean built in support for MSVC 2010, so it's probably OK to leave this as is
until the rework needed after the upgrade.