Bug 6536: Add XSLT transformation on Z3950 search results

Bug 6536: Add XSLT transformation on Z3950 search results

Use the stylesheets listed in field add_xslt of z3950servers to transform
search results of Z3950/SRU search.
Additionally, the template has been changed to make more error messages (or
warnings) visible when displaying results. Until now, error message were
shown in the results table and when connection errors occurred, no results
were displayed at all.

Test plan:
Create some stylesheets (or see the sample patch on bug 6536).
Add these stylesheets to some Z3950/SRU servers.
Do Z3950 search and verify the transformations.
Do a search with 2 targets; make one target fail (by manipulating its server
data). Do you see the connection error and the results for the other target?
Generate a XSLT error by modifying one stylesheet. Check search results. You
should see warnings.

Signed-off-by: Giuseppe Angilella <giuseppe.angilella@ct.infn.it>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@gmail.com>