8157952: Parallelize Memory Pretouch
Summary: Use multiple threads to pretouch memory using -XX:+AlwaysPreTouch to use more memory bandwidth
Reviewed-by: jmasa, sangheki

8141501: Problems with BitMap buffer management
Reviewed-by: pliden, kbarrett

8145752: Fix include guards in GC code
Reviewed-by: mgerdin, stefank

8079792: GC directory structure cleanup
Reviewed-by: brutisso, stefank, david