Ignore hidden members when counting new ones.

The Class#find_members(:local=>true) previously also returned
the hidden members.  This resulted from the fact that internally
it was using #global_by_id and #local_by_id indexes from MembersIndex
class.  As these maps are also used internally inside MembersIndex
I'm now exposing #all_global and #all_local methods which return
the arrays instead of hashes and both without any hidden members.