Bug 7973- Allow for new type of LDAP authentication

Bug 7973- Allow for new type of LDAP authentication

This patch aims to solve the LDAP bind authentication method. Here are
some considerations:

- This is a standalone patch, so all the previous submitted ones are
  rendered obsolete;
- LDAP bind authentication is now done in 3 steps:
  1 - LDAP anonymous bind;
  2 - LDAP search entry for the given username;
  3 - LDAP bind with the DN of the found entry + the given password.
- The process fails if none or more than 1 entries are found for the
  given username;
- The <principal_name> setting in koha-conf.xml isn't used anymore;
- The patch is backwards compatible, so users already using the
  previously implemented LDAP bind authentication should be able to use
  it the same.

http://bugs.koha-community.org/show_bug.cgi?id=7973

Signed-off-by: Vitor Fernandes
Signed-off-by: Dobrica Pavlinusic <dpavlin@rot13.org>
Signed-off-by: Katrin Fischer <Katrin.Fischer.83@web.de>
Passes all tests and QA script and has 2 solid sign offs.
Signed-off-by: Jared Camins-Esakov <jcamins@cpbibliography.com>