Make --enable-pthreaded-ubik do what it claims

Make --enable-pthreaded-ubik do what it claims

The configure help text for --enable-pthreded-ubik says
    "enable installation of pthreaded ubik applications"

This patch set makes the behaviour in the code match that. Instead
of controlling whether the pthreaded ubik code is compiled at all,
the configure option now just controls whether it is installed. This
means that we'll always build the pthread code, and so should reduce
the number of times it is inadvertently broken.

Change-Id: I8b2ffb46e01157f2043cf7daf68e69580ea285c5
Reviewed-on: http://gerrit.openafs.org/5028
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>