Fix a bug in passing the base path to proxied servers. (#1846)
Fix a bug in passing the base path to proxied servers. (#1846)

This change fixes a bug in the reverse proxy where the base path
(if set) was not being passed to other local servers to which
we proxied.

In particular, this meant the ungit UI could not be loaded if the
base path was set.
parthea/datalab,parthea/datalab,googledatalab/datalab,parthea/datalab,parthea/datalab,googledatalab/datalab,googledatalab/datalab,googledatalab/datalab,googledatalab/datalab,parthea/datalab,parthea/datalab,googledatalab/datalab