Initial support for C++ parameter completion

The improved completion in call context now works with:

 - Functions.
 - Member functions.
 - Constructors.
 - New expressions.
 - Function call expressions.
 - Template variants of the previous.

There are still rough edges to be fixed:

 - Provide support for optional parameters.         (fix known)
 - Provide support for member initializers.         (fix known)
 - Provide support for variadic template functions. (fix unknown)
 - Others?

llvm-svn: 226670
diff --git a/clang/include/clang-c/Index.h b/clang/include/clang-c/Index.h
index ed7bd16..925d0bf 100644
--- a/clang/include/clang-c/Index.h
+++ b/clang/include/clang-c/Index.h
@@ -2276,7 +2276,12 @@
    */
   CXCursor_ModuleImportDecl              = 600,
   CXCursor_FirstExtraDecl                = CXCursor_ModuleImportDecl,
-  CXCursor_LastExtraDecl                 = CXCursor_ModuleImportDecl
+  CXCursor_LastExtraDecl                 = CXCursor_ModuleImportDecl,
+
+  /**
+   * \brief A code completion overload candidate.
+   */
+  CXCursor_OverloadCandidate             = 700
 };
 
 /**