[Fixes #55] Migrates to Guava 17.0

- Removes use of deprecated closeQuietly (now "considered harmful")
- Migrates from InputSupplier to ByteSource and CharSource

The behavior of Resources.getResource() also seems to have changed
subtlely between 13.0 and 17.0; the maven plugin now explicitly
sets the current thread's context ClassLoader to ensure that
Resources.getResource() finds packages during namespace construction
and testing.

We should probably still move towards our own repackaged version
of guava to avoid the risk of version conflict for those who are
using Renjin together other libraries which may require different
versions of Guava.

This is what jersey does:
https://github.com/jersey/jersey/tree/master/bundles/repackaged/jersey-guava

See discussion of closeQuietly deprecation:
https://code.google.com/p/guava-libraries/issues/detail?id=1118