Bug 25416: Let OPAC XSLTs know if the context is an anonymous session

Bug 25416: Let OPAC XSLTs know if the context is an anonymous session

This patch makes use of the 'variables' parameter in XSLTParse4Display
method in the different places that it is used in the OPAC. It does by
passing this parameter with

    anonymous_session => 1|0

The value will depend on the output from get_template_and_user (i.e. if
there's a returned borrowernumber).

A special case takes place in search results, as the call to
XSLTParse4Display happens in C4::Search::searchResults. So a new
parameter 'xslt_variables' is added to it.

To test:
1. Apply the [DO NOT PUSH] patch
2. Open the OPAC in your browser
3. Try detail pages, search results, tags and lists/shelves pages with
   or without an active session
=> FAIL: It always says (somewhere) 'Anonymous session: Yes'
4. Apply this patch, restart_all
5. Repeat 3
=> SUCCESS: It will tell the Yes/No correctly regarding anonymous
sessions!
6. Sign off :-D

Sponsored-by: Universidad ORT Uruguay
Signed-off-by: Victor Grousset/tuxayo <victor@tuxayo.net>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Joy Nelson <joy@bywatersolutions.com>