Summary: Added new product ObjectAlignmentInBytes flag to control object alignment.
Reviewed-by: twisti, ysr, iveresov

6902115: G1:assert(ignore_max_completed||thread->is_Java_thread()||SafepointSynchronize::is_at_safepoint())
Summary: Remove invalid assert and mangle filler objects in TLABs that are being retired.
Reviewed-by: ysr, jmasa