Feature/10507 fix clang warnings

I fixed or suppressed many compiler warnings from AppleClang on OSX. 

for testing: code review, verify that targets "all" and "AllTests" now build cleanly with AppleClang on OSX and this doesn't create new errors or warnings on the build servers.

This is a continuation of pull request #63 
http://trac.mantidproject.org/mantid/ticket/10507