Parsing and basic structure of try_apply. Not yet properly

threaded into IRGen; tests to follow when that's done.

I made a preliminary effort to make the inliner do the
right thing with try_apply, but otherwise tried to avoid
touching the optimizer any more than was required by the
removal of ApplyInstBase.

Swift SVN r26747

lib/SILAnalysis/ValueTracking.cpp

@@ -53,6 +53,7 @@ static bool isTransitiveEscapeInst(SILInstruction *Inst) {
   case ValueKind::AllocValueBufferInst:
   case ValueKind::BuiltinInst:
   case ValueKind::ApplyInst:
+  case ValueKind::TryApplyInst:
   case ValueKind::WitnessMethodInst:
   case ValueKind::CopyAddrInst:
   case ValueKind::RetainValueInst: