liboafs_util: export symbols for tabular_output

Otherwise compilation fails on AIX.

Change-Id: Id22b7726d9aa56f9a2e0665257b3099baf774896
Reviewed-on: http://gerrit.openafs.org/10326
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>