[SAC] LDAP creation script re-enabled, git-managed and easier to disable

[Sandro Santilli]

(1)
I've tweaked the user registration form to print the contents
of a MAINTAINANCE file if found, so we don't need to mess with
symlinks again, and it can be easier to write info about the
kind of maintainance and instructions about what to do in those
periods.

(2)
I've put all the cgi-bin directory under a local git repository
as I haven't figured out how to access the SVN repository.

(3)
I've enabled user registration again, as it was needed by a GSOC
student. Disabling it again is just a matter of adding this
MAINTAINANCE somewhere.

--strk;