Fixup the PrepareResources task to properly augment the classpath in the exclusives regime.

+ Undo pingpong example workaround.
+ Perform minor cleanups on exclusives related code read to grok this fix.

Addresses these issues:
+ https://github.com/twitter/commons/issues/160
+ https://github.com/twitter/commons/issues/163
+ https://github.com/twitter/commons/issues/170