Patch guice library to fix NPE in some corner cases

Currently used guice version (3.0) has a bug which triggers an NPE when
2 modules add different bindings to a same instance.
This is fixed by commit 6b7e7187bd07 in guice repository, scheduled to be
included in Guice 3.1 release.
See http://code.google.com/p/google-guice/issues/detail?id=473 for details.
Since Guice 3.1 library is bigger and includes quite significant changes,
out of compatibility concerns we just patch our current Guice version (3.0)
with this patch.