[analyzer] When reporting a leak in RetainCount checker due to an early exit from...

[analyzer] When reporting a leak in RetainCount checker due to an early exit from init, step into init.

The heuristic here (proposed by Jordan) is that, usually, if a leak is due to an early exit from init, the allocation site will be
a call to alloc. Note that in other cases init resets self to [super init], which becomes the allocation site of the object.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179221 91177308-0d34-0410-b5e6-96231b3b80d8