8160399: is_oop_or_null involves undefined behavior
8164984: Improper use of is_oop in production code
Summary: replace oop->is_oop*() with oopDesc::is_oop*(oop) so this pointer can be verified
Reviewed-by: iklam, kvn, dholmes

8134626: Misc cleanups after generation array removal
Reviewed-by: david, dholmes, tschatzl

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