Escape the LDAP search string instead of truncating it.

Escape the LDAP search string instead of truncating it.

A few characters must be escaped in a LDAP search string. Sarg used to
truncate the user login name at the first "dubious" character found in
the string and the list of "dubious" character was much longer than
necessary. Instead of truncating the user login, this patch escape the
characters.