The LWG 3506 issue ads allocator-extended versions of the constructors
that take iterator arguments.

Signed-off-by: Jonathan Wakely <jwakely@redhat.com>

libstdc++-v3/ChangeLog:

	* include/bits/stl_queue.h (priority_queue): Add
	allocator-extended overloads for constructors taking iterator.
	* testsuite/23_containers/priority_queue/lwg3506.cc: New test.

Tested powerpc64le-linux. Committed to trunk.