Bug 13913 - Renewal error message in OPAC is confusing

Bug 13913 - Renewal error message in OPAC is confusing

This patch adds some formatting to the error message a patron receives
when there are renewal failures in the OPAC.

This is pretty much the least which could be done to address this
problem. However, I don't think the issue can be fixed without
re-thinking how renewals are processed. Sending error messages back to
opac-user.pl via URL parameter isn't flexible enough.

To test, apply the patch and attempt to renew multiple items in the OPAC
which cannot be renewed for some reason, for instance because they have
been renewed too many times. The error messages should appear in a list
rather than strung together in one long block of text.

Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>