Added Head method to IRestClient.  Updated implementation on
ServiceClientBase. Added HEAD verb to several conditional checks in a few
files for 1) enabling use of a query string and 2) to prevent the use of a request body
when submitting HEAD requests (which currently throws a
ProtocolViolationException).
Merge remote-tracking branch 'upstream/master'
Changed Head methods on IRestClient to return HttpWebResponse objects
directly.
Merge remote-tracking branch 'upstream/master'
Merge pull request #394 from electricshaman/master

Further bugfixes when using CustomMethod for Head method