Request for review (xs) 8006040: NPG: on_stack processing wastes space in ConstantPool

[Coleen Phillimore]

Summary: Added on_stack bit to _flags.  Also MetadataMarkOnStack is used 
for more than JVMTI so had to be moved.

Confirmed with John and Chris that setting invokedynamic bits doesn't 
require atomic operations so I can add on_stack to the flags.

open webrev at http://cr.openjdk.java.net/~coleenp/8006040/
bug link at http://bugs.sun.com/view_bug.do?bug_id=8006040

Tested NSK quick.testlist and runThese.

Thanks,
Coleen