Request for reviews (M): 6924259: Remove String.count,String.offset fields

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/6924259/webrev

6924259: Remove String.count/String.offset

Allows a version of the String class that doesn't have count,offset fields.
These VM changes works with both versions of String class by checking the 
presence of fields.

Initial changes were done by Brian and Tom years ago. I addapted it for current 
sources and tested it.

Tested with NSK, regression tests, CTW, refworkload, CDS (class sharing).

Thanks,
Vladimir