Added a new API to SBFrame:

lldb::addr_t SBFrame::GetCFA();

This gets the CFA (call frame address) of the frame so it allows us to take an address that is on the stack and figure out which thread it comes from.

Also modified the heap.py module to be able to find out which variable in a frame's stack frame contains an address. This way when ptr_refs finds a match on the stack, it get then report which variable contains the pointer.

llvm-svn: 238393