6743188: incomplete fix for 6700047 C2 failed in idom_no_update
Reviewed-by: rasbold

The fix for 6700047 only checks the direct control of the node which
is insufficient to fix this in all cases. During a conversation with
Ross he mentioned that his original intent was to stop further loop
optimizations but the way it was structured it only stopped it for
contained loops. I decided the best fix was to make it really stop
further loop optimizations instead of trying to correct the cloning
logic. I removed the change from loopopts.cpp that tried to find a
better placement. This leaves that logic effectively the same as
before though I kept the restructuring I did since I think it's
cleaner. The original fix can be viewed at
http://hg.openjdk.java.net/jdk7/hotspot-comp/hotspot/rev/020a0b730379.
iteration split now returns a flag indicating whether to continue
optimization. I also updated the test case.