decl.c (grokparms): Added new error for duplicate function parameters names in function prototypes...

	* cp/decl.c (grokparms): Added new error for duplicate function
	parameters names in function prototypes, to match gcc behavior.

	* testsuite/g++.dg/other/error15.C: New.
	* testsuite/g++.dg/cpp0x/variadic-ex9.C: Renamed function parameter to
	avoid triggering a "multiple parameters named" error.

From-SVN: r124083