RFR: cleanup - removed unneeded casts in jdi

[Egor Ushakov]

Hi all,

could you please review and sponsor this small cleanup removing unneeded 
casts in jdi LocationImpl and MirrorImpl.
They were preventing creating custom Location and Mirror implementations 
used for tests and IDEA debugger impl.
http://cr.openjdk.java.net/~avu/egor.ushakov/cast_fix/

I do not have rights to create JDK bug report directly, please create it 
if it is needed for the procedure.

Thanks!

-- 
Egor Ushakov
Software Developer
JetBrains
http://www.jetbrains.com
The Drive to Develop