User simpler stub

Better error message if zlib is not compiled in (any recent PHP has it
in).
Revert "This would create an existing directory."

This reverts commit cf04b9b01b71fccb9eb5154e99924fabe251c66b.

The code is wrong, but the theory is correct (we don't currently use
nested directories, but we might in the future).
Correct makedir() argument