Fix get with body in ClientStatic

Changed ClientStatic to correctly accept a body. Before it was trying
to call setBody which didn't exist. Unit test added.

This change may be controversial as there is debate as to wether GET's
should have a body or not. However, the documentation for this class
says it is supported, so this fixes that broken functionality.
Merge pull request #4376 from robertprice/ClientStatic-GET-with-body

Fix get with body in ClientStatic
Merge branch 'hotfix/4376'

Close #4376