added a uid_wrapper library

[tridge at samba.org]

Hi Andrew,

 > Why are the 'this does not work with UID wrapper' checks compile-time,
 > rather than run-time?  As it is, this means we can't turn off all the
 > changes at run-time.

yep, good point. I've fixed it.

 > Also, shouldn't the 'skip' on the check in directory_create_or_exist()
 > should just be on the UID value, not on the permissions?

also fixed, thanks!

Cheers, Tridge