Pls review 7124880 (XS)

[Paul Hohensee]

The framework implemented for

7117389: Add a framework for vendor-specific command line switch 
extensions to Hotspot

did not include support for vendor-specific manageable-by-JMX switches.
This change adds new methods Flag::is_external_ext() and 
Flag::is_writeable_ext() that
return false, and uses them in Flag::is_external() and 
Flag::is_writeable().  Somewhat
relatedly, management.cpp didn't include globals.hpp, even though it 
uses Flag methods.
I added globals.hpp to its #include list for completeness, even though 
it was being
included indirectly.

Webrev here

http://cr.openjdk.java.net/~phh/7122880.00/

Thanks,

Paul