[patch][google] Backport r176665 to google/gcc-4_6 making narrowing conversions a pedwarn.

I'm backporting this so that, if we run into a particularly obnoxious set of narrowing conversions in the C++11 transition, we can just -Wno-narrowing instead of rolling a new gcc release.

c-family/ChangeLog.google-4_6:
2011-11-02  Jeffrey Yasskin  <jyasskin@google.com>

	Backport from rev 176665

	2011-07-22  Jason Merrill  <jason@redhat.com>

		* c.opt (Wnarrowing): New.

cp/ChangeLog.google-4_6:
2011-11-02  Jeffrey Yasskin  <jyasskin@google.com>

	Backport from rev 176665

	2011-07-22  Jason Merrill  <jason@redhat.com>

		* typeck2.c (check_narrowing): Downgrade permerror to pedwarn.
		Make conditional on -Wnarrowing.

testsuite/ChangeLog.google-4_6:
2011-11-02  Jeffrey Yasskin  <jyasskin@google.com>

	Backport from rev 176665

	2011-07-22  Jason Merrill  <jason@redhat.com>

		* g++.dg/cpp0x/initlist55.C: New.