tree-ssa-threadedge.c (thread_across_edge): Do not allow threading through joiner blocks with abnormal outgoing edges.

	* tree-ssa-threadedge.c (thread_across_edge): Do not allow threading
	through joiner blocks with abnormal outgoing edges.

	* tree-ssa-threadupdate.c (thread_block_1): Renamed from thread_block.
	Add parameter JOINERS, to allow/disallow threading through joiner
	blocks.
	(thread_block): New.  Call thread_block_1.
	(mark_threaded_blocks): Remove code to filter out certain cases
	of threading through joiner blocks.
	(thread_through_all_blocks): Document how we can have a dangling
	edge AUX field and clear it.

From-SVN: r203975