Code changes to reduce number of warning messages.

Code changes to reduce the number of warnings that are generated
when sass code is run as part of the sinatra test suite.

This should also reduce the number of warnings generated in other
softwares' test suites.

Although some of the changes may make the code a bit less 
'clean' I think it is important for well-used libraries to try and be good 
citizens and keep the number of warnings down.

This pull request fixes a lot of the low-hanging stuff.