Compiler classpath and DiagnosticCollector

[rlsutton1]

adds ability to set and use a DiagnosticCollector adds ability to set options, such as a class path changed source version to 1.7

[verhas]

Please remove the formatting change and follow the suggestions I gave about style (mainly have if/than/else structures explicitely rather than 'set default here instead of else branch / if/then return and omit else / return error'.

If you do that I will be more than happy to merge your changes into the project. These changes seem to be very good.

And a last comment: If there is any change in the code and there is no change in the test it means the quality of the code degraded. Create new test cases that test your changes.