Bug 3098 follow-up: Clean up formatting

Bug 3098 follow-up: Clean up formatting

This patch cleans up the formatting of the 856 display code in
MARC21slim2OPACDetail.xsl. Tabstops are correct, and the OPACURLOpenInNewWindow
syspref check is moved to control the use of a 'target="_blank"' attribute,
rather than having two blocks of almost-identical code.

Signed-off-by: Nicole C. Engard <nengard@bywatersolutions.com>
Signed-off-by: Chris Cormack <chrisc@catalyst.net.nz>
(cherry picked from commit 009036b53722881f607ed01b5701bd300abd6735)

Signed-off-by: Chris Nighswonger <chris.nighswonger@gmail.com>