Migrate Sema::ActOnCallExpr to Sema::FixOverloadedFunctionReference,

so that we maintain better source information after template argument
deduction and overloading resolves down to a specific
declaration. Found and dealt with a few more cases that 
FixOverloadedFunctionReference didn't cope with.

(Finally) added a test case that puts together this change with the
DeclRefExpr change to (optionally) include nested-name-specifiers and
explicit template argument lists.

llvm-svn: 84974