Request for reviews (XS): 7047300: VM crashes with assert(_base == InstPtr) failed: Not an object pointer

[Vladimir Kozlov]

http://cr.openjdk.java.net/~kvn/7047300/webrev

Fixed 7047300: VM crashes with assert(_base == InstPtr) failed: Not an object 
pointer

The code incorrectly used is_instptr() instead of is_oopptr() to get const_oop.
Tested with failed jck test.