Don't link plugin_select twice

- Remove plugin-select.c from source file list
- Make select lib PIC

Change-Id: I962e0fb0c9a08c567b715a53ed9b9675d16ff09e
Reviewed-on: http://review.couchbase.org/33352
Reviewed-by: Brett Lawson <brett19@gmail.com>
Tested-by: Mark Nunberg <mnunberg@haskalah.org>