Code review request (Backport): 7199092: NMT: NMT needs to deal overlapped virtual memory ranges

[Zhengyu Gu]

This change is already in JDK8. The purpose of this request is to review 
the merge conflicts during backporting to 7u12.

The complete webrev:  
http://cr.openjdk.java.net/~zgu/7199092/webrev.backport/

The conflicts are in the two files:

*src/share/vm/memory/genCollectedHeap.cpp*
*src/share/vm/memory/filemap.cpp

*mainly for dealing with class data sharing memory regions.

Thanks,

-Zhengyu