[LLVMdev] small patch to add an assert to PATypeHolder

[Erick Tryzelaar]

Hello,

I ran into an issue with the ocaml bindings where PATypeHolder was getting a
null pointer, which eventually caused a segfault. This patch copies what
PATypeHandle does and adds the assert in the PATypeHolder::addRef method.

Also, I'm using git's gateway to subversion to track llvm and send this
patch. The patch applies fine according to my tests, but if there are any 
problems, I'll find a better way to do this.

-e