6362677: Change parallel GC collector default number of parallel GC threads. Summary: Use the same default number of GC threads as used by ParNewGC and ConcMarkSweepGC (i.e., the 5/8th rule). Reviewed-by: ysr, tonyp

6642634: Test nsk/regression/b6186200 crashed with SIGSEGV Summary: Use correct allocation path in expand_and_allocate() so object's mark and p-bits are set as appropriate. Reviewed-by: jmasa, pbk