Updated plovr so that `ant clean jar test` works again.

This is after updating to the latest version of the
Closure Compiler, which uses Guava 14 instead of 13.

A handful of plovr source files had to be updated because
Closeables.closeQuietly is deprecated in Guava 14, and
plovr is designed to compile without warnings.

The Closure Stylesheets JAR that was bundled with plovr
included a copy of Guava 13, so we had to change to
building it from source so that it could be compiled
against Guava 13, as well.

plovr is also building in Eclipse using this new setup.