Add variable to define if a share should be hidden.

Add variable to define if a share should be hidden.

If you create a share on a Windows machine called foo$ then this share is
of the type STYPE_DISKTREE. So it is possible to administrate this kind of
share. Tested on Windows NT and 2003.

In samba we assume that if a share with a $ at the end must be of the type
STYPE_DISKTREE_HIDDEN. This is wrong, so we need a variable in the config
to define if the share should be hidden or not.