Use proxy only if the scheme is http and it points to an internal resource.

Proxies should not intervene in schemes other than http or in the http schemes
that contain a dot.  We are assuming that dot is an illegal character for the
shortname of the nodes or the master.  With this fix, test_ddfs should pass on
the local cluster.
Merge pull request #420 from pooya/shayan/light

Use proxy only if the scheme is http and it points to an internal resour...