Moved Kernel::System::User to use bind variables

Also I added a few unit tests for UserSearch().
These unit tests would not work on SQL Server before; but now
because of the bind variables they do.
Follow-up fix for bug#9921 - Reply to previously signed email breaks PGP verification.

-reworked regular expressions
Fixed: DefaultOverviewColumns under Ticket -> Frontend::Agent Wrong Description (bug#9933).
Follow-up fix for bug#7008
Product.xml is now eval'ed to be valid XML.

If OTRS is behind a proxy with a landing page, the Product.xml
file is not valid XML.
This commit puts the parsing of the XML in an eval{} so that if
this fails the dashboard is still displayed.

This fixes bug#9935 - http://bugs.otrs.org/show_bug.cgi?id=9935
Replaced DB Quote() functions with DB Bindings in CustomerCompany Backend.
Fixed: Activity-Dialogs in wrong order (bug#9937).
Merge remote-tracking branch 'upstream/master' into otrs-master