RFR: Add asserts all over synchronizer

[Roman Kennke]

I've seen an assert in synchronizer, and want to make sure than
whenever the mark word is modified by synchronizer, the object really
is in to-space and safe to write. This patch adds assert all over the
place, wherever the mark word is modified by synchronizer and biased
locking. I hope I found all the places...

http://cr.openjdk.java.net/~rkennke/assertsynchronizer/webrev.00/

Ok to push?

Roman