Work-in-progress implementation of C++0x [temp.arg.explicit]p9, which

allows an argument pack determines via explicit specification of
function template arguments to be extended by further, deduced
arguments. For example:

template<class ... Types> void f(Types ... values);
void g() { 
  f<int*, float*>(0, 0, 0);   // Types is deduced to the sequence int*, float*, int
}

There are a number of FIXMEs in here that indicate places where we
need to implement + test retained expansions, plus a number of other
places in deduction where we need to correctly cope with the
explicitly-specified arguments when deducing an argument
pack. Furthermore, it appears that the RecursiveASTVisitor needs to be
auditied; it's missing some traversals (especially w.r.t. template
arguments) that cause it not to find unexpanded parameter packs when
it should.

The good news, however, is that the tr1::tuple implementation now
works fully, and the tr1::bind example (both from N2080) is actually
working now. 

llvm-svn: 123163