[analyzer] Fix a false positive of the 'self' initialization checker.

A common pattern in classes with multiple initializers is to put the
subclass's common initialization bits into a static function that receives
the value of 'self', e.g:

   if (!(self = [super init]))
     return nil;
   if (!(self = _commonInit(self)))
     return nil;

It was reported that 'self' was not set to the result of [super init].
Until we can use inter-procedural analysis, in such a call, transfer the
ObjCSelfInitChecker flags associated with 'self' to the result of the call.

Fixes rdar://8937441 & http://llvm.org/PR9094

llvm-svn: 124940