[dev] Horde Group_hooks class updates

[Edward Rudd]

As I'm setting up my horde 3 install I am using the Group_hooks class to
hook into the existing LDAP groups I already have. (Eventually I should
probably just write a Group_ldap driver)

I've added 3 more hooks to the driver but while working on it I noticed
a small issue when you have a group with spaces in the name it will never
be able to find the _group_hook_Group_Name function.   

So My question is what would be a good way to munge the groupname and
later un-munge it in the getGroupMemberships function? (which the current
implementation won't actually work, I'm fixing that as well).. 

I'll be submitting my patch when I'm all completed with it later today. I
just wanted some input on it as right now the munging for group names is
to replace the group tier separator ':' with two '_'s, (which needs to be
un-done in the getGroupMemberships function). I was thinking of just
replacing a space with an '_' but then it would not be easy to un-munge
the groupname in the getGroupMemberships function if the group name had
legitimate '_'s in it.