RFR: JDK-8235846: Improve WindbgDebuggerLocal implementation

[Alex Menkov]

Hi all,

Please review a fix for
https://bugs.openjdk.java.net/browse/JDK-8235846
webrev:
http://cr.openjdk.java.net/~amenkov/jdk15/WinDbg_improve/webrev.01/

Main goal of the change is to improve error reporting (we have several 
bugs and need at least COM error codes for WinDbg calls).
Also the fix improves/rearranges this quite old code.

--alex