Grabs the ClientIp from X-Forwarded-For or REMOTE_ADDR
before falling back to UserHostAddress.

Adapted from @nicholashead's PR here:
https://github.com/MindscapeHQ/raygun4net/pull/149
Actually call the new method.
Ported GetIpAddress to Raygun4Net .Net 2.0
Ported GetIpAddress to Raygun4Net .Net 4.5
Merge pull request #154 from MindscapeHQ/get-forwarded-addr

Grabs the ClientIp from X-Forwarded-For or REMOTE_ADDR