[PDB] Better native API support for pointers.

[PDB] Better native API support for pointers.

We didn't properly detect when a pointer was a member
pointer, and when that was the case we were not
properly returning class parent info.  This caused
member pointers to render incorrectly in pretty mode.
However, we didn't even have pretty tests for pointers
in native mode, so those are also added now to ensure
this.

llvm-svn: 343393