Default gimple_outgoing_range to not process switches.

Default gimple_outgoing_range to not process switches.

Change the default constructor to not process switches, add method to
enable/disable switch processing.

	* gimple-range-edge.cc (gimple_outgoing_range::gimple_outgoing_range):
	Do not allocate a range allocator at construction time.
	(gimple_outgoing_range::~gimple_outgoing_range): Delete allocator
	if one was allocated.
	(gimple_outgoing_range::set_switch_limit): New.
	(gimple_outgoing_range::switch_edge_range): Create an allocator if one
	does not exist.
	(gimple_outgoing_range::edge_range_p): Check for zero edges.
	* gimple-range-edge.h (class gimple_outgoing_range): Adjust prototypes.