[NEXUS-6611] Rebuild yum test rpms with > 1 files and includes specs for reference
POC: require explicit bindings for core+plugins; can help find broken/incorrect bindings.
Also verify latest Guice build (3.2.2) which includes various fixes and support for Java8.

http://google-guice.googlecode.com/git/latest-api-diffs/3.0/javadoc/com/google/inject/Binder.html#requireExplicitBindings()
Apply requireExplicitBindings to core and non-Plexus plugins, fix a few places that assumed just-in-time bindings