LP#1576727: Delimit bib CN subfields with a space

LP#1576727: Delimit bib CN subfields with a space

When suggested call numbers are pulled from a bib record, space delimiters are
dropped.  This is bad for noralization routines.  Now we will forcibly inject
a space between subfield values.

Also included are two small optimizations: exit early if no nodes are found
for a particular bib CN definition; use map+join instead of a for loop and
blind substring trim to stitch together an xpath expression.

Signed-off-by: Mike Rylander <mrylander@gmail.com>
Signed-off-by: Cesar Velez <cesar.velez@equinoxinitiative.org>