Merging r155576:

------------------------------------------------------------------------
r155576 | akirtzidis | 2012-04-25 11:39:17 -0700 (Wed, 25 Apr 2012) | 4 lines

When resolving default template arguments, it should be done in the declaration context
of the template what we are going to instantiate.

Fixes various crashes of rdar://11242625 & http://llvm.org/PR11421.
------------------------------------------------------------------------

llvm-svn: 155582