Performance Enhancement for MockHandler : Search matchers once instead of twice

MockHandler currently calls these 2 methods in quick succession when
providing the stubbed result for an invocation:

mockitoStubber.hasResultFor(invocation)
mockitoStubber.getResultFor(invocation)

Unfortunately this involves duplication of work, because both methods call
findMatch(invocation), which in turn will search *all* of the stubbed
invocations against this mock instance. The search is performed twice, when
it only needs to be performed once.

See: http://code.google.com/p/mockito/issues/detail?id=19