Summary: Remove -XX:+CacheTimeMillis option and associated functionality
Reviewed-by: acorn, never

Summary: Mangling the unused space is having an adverse affect on testing with fastdebug builds so turn it off by default.
Reviewed-by: ysr, tonyp

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