Add range erase, element insert, and range insert methods to

TinyPtrVector. With these, it is sufficiently functional for my more
normal / pedestrian uses.

I've not included some r-value reference stuff here because the value
type for a TinyPtrVector is, necessarily, just a pointer.

I've added tests that cover the basic behavior of these routines, but
they aren't as comprehensive as I'd like. In particular, they don't
really test the iterator semantics as thoroughly as they should. Maybe
some brave soul will feel enterprising and flesh them out. ;]

llvm-svn: 161104