Bug 20910: Display 773$g when $0 is present too

Bug 20910: Display 773$g when $0 is present too

This patch makes the XSLT logic add the $g subfield in the 773 display
in both the OPAC and staff interface MARC21 record detail pages.

The XSLT chooses between different ways to create the link for the
related content, but then it only adds the $g in two of the cases.
There's no obvious reason for a different display.

To test:
- Have  a record with:

=773   $tHost title $gp4.

=> SUCCESS: Notice the Detail view shows:
  In: Host title p4.

- Have another record with:

=773   $tHost title $gp4. $w100
- Enable UseControlNumber (only to cover the case):
=> SUCCESS: Notice the detail view shows
  In: Host title p4.

- Have another record with:

=773   $tHost title $gp4. $0456

=> FAIL: The Detail view doesn't show p4.
- Apply this patch
- Reload
=> SUCCESS: The Detail view displays p4.!
- Sign off :-D

Sponsored-by: Escuela de Orientacion Lacaniana
Signed-off-by: Jesse Maseto <jesse@bywatersolutions.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
(cherry picked from commit f161d4e823aa84d7c602089eacacbdf2bfc502ce)
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>