RefCountedBaseVPTR needs the IntrusiveRefCntPtrInfo as friend,

now that this handles the release / retain calls.

Adds a regression test for that bug (which is a compile-time
regression) and for the last two changes to the IntrusiveRefCntPtr,
especially tests for the memory leak due to copy construction of the
ref-counted object and ensuring that the traits are used for release /
retain calls.

llvm-svn: 149411