build: more configure summary

Improved configure summary, including a check for namei fileserver mode.

Change-Id: Id5117ae8c27126c56e28eb3ab7f6e8ef7fd0558d
Reviewed-on: http://gerrit.openafs.org/10372
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>