libafsauthent: export ugen_ClientInit*

libafsauthent: export ugen_ClientInit*

Windows was only exporting the bare version and not the Cell/Flags/Server
versions; Unix was exporting none of them.

These routines for obtaining a ubik client are more generic than the
historical (and already exported) ubik_ClientInit routine, allowing for
the use of an alternative configuration directory, additional flags,
and the like.

Change-Id: I6577ef5f95d2b801c049befa9fddd3b605ff80f5
Reviewed-on: https://gerrit.openafs.org/13130
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>