Function:   SYMKDIR( <expC1> ) --> integer

Synopsis:   Creates a subdirectory.

            <expC1> is string naming the new subdirectory

Notes:      <expC1> should be a string such as You would use when
            creating a subdirectory in the DOS environment with
            the DOS command "MD" or "MKDIR".

Returns:    0 if subdirectory created succesfully,
            any number less than 0 on error.