(CFACT-137) Restrict Boost.Locale to Windows

Boost.Locale's locale generator is only needed on Windows to generate a
UTF-8 compatible default. Restrict linking while we generate new Boost
libraries for other platforms.
Merge pull request #236 from MikaelSmith/bug/master/CFACT-137-restrict-locale

(CFACT-137) Restrict Boost.Locale to Windows