Add Unicode support to msys-core

This ports in Karsten Blees' Unicode patches, and makes a few minor
changes to build within mingwport.  The resulting msys-1.0.dll is
able to properly handle Unicode characters -- it is possible to
rebuild msys-bash after, but doesn't appear to be necessary.

After this patch (and updating msys-1.0.dll), I found that the only two remaining failed tests were t1508-at-combinations (which uses some really funny branch names), and t5510-fetch (which uses rsync).  So, this seems pretty critical to the overall goal of getting all unit tests passing!