Fix false positives for for-loop-analysis warning

Summary:
For PseudoObjectExpr, the DeclMatcher need to search only all the semantics
but also need to search pass OpaqueValueExpr for all potential uses for the
Decl.

Reviewers: thakis, rtrieu, rjmccall, doug.gregor

Subscribers: xazax.hun, rjmccall, doug.gregor, cfe-commits

Differential Revision: http://reviews.llvm.org/D17627

llvm-svn: 263087