volser: Tidy header includes

volser: Tidy header includes

Since we adopted libroken, we get a lot of header includes automatically
from roken.h. Use these, instead of including lots of things multiple
times.

Also, add sys/uio.h to the list of libraries that we check for.

Change-Id: I03d9c143db42a1ec415ab5624e2cbede0d34e310
Reviewed-on: http://gerrit.openafs.org/4318
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>