Added patch for muParser

This patch corrects the thousands separator behavior when muparser is built against libc++. More information is in the thread link below. Changes to muParserBase.h have already been added to the trunk and the developer notified that this same line also appears in muParserInt.h.

Will the bottle be automatically updated?

https://groups.google.com/d/topic/muparser-dev/l8pbPFnR46s/discussion
If there is an upstream commit for this can you link to it as a comment (and, ideally, use it as the patch)? If not, no worries.