review(S) 7004547: regular loop unroll should not unroll more than max unrolling

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7004547/webrev

Fixed 7004547: regular loop unroll should not unroll more than max unrolling

Max unroll policy when calculating new loop body size does not take into account 
that after unroll conjoined loop's head and tail will fold. As result there are 
cases when max unroll was not done but regular unroll will do full unrolling for 
main loop.
Use long arithmetic to calculate exact trip count.
Add missing nodes limit check for loop split (pre-main-post).