begin fixing clang warnings

I'm starting to eliminate compiler warnings from AppleClang on OSX. This pull request doesn't fix all of them, but does get the number to a more manageable level.

for testing: code review and verify there are fewer warning produced by AppleClang on OS X and this doesn't create new errors or warnings on the build servers. 

http://trac.mantidproject.org/mantid/ticket/10507