[SONARPLUGINS-3111] Added PreAuthentication to Sonar LDAP

Hi

I added preauthentication support to the sonar ldap plugin as requested in [SONARPLUGINS-3111] [1].

It can be enabled by adding the following property to the sonar.properties config file:

    ldap.preauthentication=true

Or for multiserver environment:

    ldap.server1.preauthentication=true

Thank you for pulling it into the next version of sonar ldap.

[1]: http://jira.codehaus.org/browse/SONARPLUGINS-3111  "SONARPLUGINS-3111"