Improve memcapability test suite
Improve memcapability test suite

* Remove test of illegal commands in memcapable

  Users should be able to extend the binary protocol with their own commands,
  and as long as they don't change the semantics on the defined commands the
  server is memcapable even if it supports additional commands.

* Allow memcached servers to cork quiet get commands


Distrotech/libmemcached,bigbes/libmemcached,Distrotech/libmemcached,Distrotech/libmemcached,bigbes/libmemcached,bigbes/libmemcached