ldapfull: Check for ldap group membership on login

Administrators can now supply a <group_dn> configuration directive. If
it is given, only users who are members of this group will be allowed to login

Signed-off-by: Tomasz Sterna <smoku@dcclabs.tv>
Grammear, spelling and other fixes for clarity.
Fixed out-conn-reuse s2s.xml option naming
Merge missed commit

Looks like commit:dc7e44ec99aaf1737c448695fc74c21b0e71fe34 was dropped with  some 'git push -f master'
Fix compilation errors introduced by -Werror