This function returns the names of all files contained in the
specified directory. If 'path' doesn't end with '/' either an
empty array is returned if nothing with that name exists or
an array containing the name if it exists. If 'path ends with
'/' 0 is returned if 'path' isn't a directory else the contents
of that directory as an array is returned. It is possible to
use wildcards like:
get_dir("/a*") Would return all files starting with
'a' in the muds root directory.
The function is subject to the rules defined by the function
`valid_read()'.