Additions to the cleanup branch for 50D and dot_tune

Created originally on Bitbucket by ayshih (Albert Shih)

Was already merged in Bitbucket before import, marked as merged by the import user

For tacking on to pull request #435 (closed), here's my stab at cleaning up all the current warnings for the 50D and the dot_tune module. Some of the extern declarations may be better put in header files, and vice versa.