[PMC] When creating a PMCProxy for a native PMC, cache the proxy object only if there isn't one already.  Likewise, only extract methods from the namespace when caching the PMCProxy.
[PMC] When creating a PMCProxy for a native PMC, cache the proxy object only if
there isn't one already.  Likewise, only extract methods from the namespace
when caching the PMCProxy.

This avoids a slow memory leak which resulted from performing both operations
on each PMCProxy instantiation.  See RT #47572 from Mehmet Yavuz Selim Soyturk.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@22957 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot,ashgti/parrot