Reinsert code to extract size_x and size_y parameters from GetHomeRegion response in UserAgentServiceConnector.

This is actually code from commits afb2e07 and cf61cdf
For as yet unexplained reasons, the section of these commits which changed UserAgentServiceConnector.cs disappeared from its history between approx Feb 5 2014 and Feb 13 2014.
This ought to be impossible.  More details to follow in opensim-dev mailing list