Actual use location information when looking for local variables.

This addresses the bulk of <rdar://problem/15344950>, which involes us
not being able to find local variable declarations in expressions when
the parser didn't pre-bind them for us.

The fix to name lookup itself insures that a case such as 
  case (var a, a)

doesn't allow the second 'a' to find the first.


Swift SVN r9858

lib/AST/NameLookup.cpp

@@ -280,8 +280,10 @@ struct FindLocalVal : public StmtVisitor<FindLocalVal> {
     if (!IntersectsRange(S->getSourceRange()))
       return;
     for (auto Label : S->getCaseLabels()) {
-      for (auto P : Label->getPatterns())
-        checkPattern(P);
+      for (auto P : Label->getPatterns()) {
+        if (!IntersectsRange(P->getSourceRange()))
+          checkPattern(P);
+      }
     }
     visit(S->getBody());
   }