requireExplicitBindings() method should support requiring explicit binding on individual classes

_From [glenviewjeff](https://code.google.com/u/110087215095127878251/) on July 19, 2012 16:32:35_

I'm using a couple of different injectors and I want to ensure I don't accidentally access a class that's bound automatically from an injector, especially since its scope is important.

For instance if I have a method Foo that is "illegally" requesting a Bar:

class Bar { `@`Inject Bar() {} } // Shouldn't be accessible in Foo's injector
class Foo { `@`Inject Foo(Bar bar) {} } // Binding should fail here

Apparently, the only way to do this presently is to force a run-time error with a provider method.

I'd like Guice support to force an automatic binding to fail only on a specific class.  I think it could work via requireExplicitBindings() with variable length parameter list of classes to prohibit.

_Original issue: http://code.google.com/p/google-guice/issues/detail?id=716_