NAME
        UnLoadSeg -- Unload a seglist previously loaded by loadseg()

    SYNOPSIS
        success = UnLoadSeg( seglist )
        D0                     D1

        bool unloadseg(bptr)

    FUNCTION
        Unload a seglist loaded by loadseg().  'seglist' may be zero.
        Overlaid segments will have all needed cleanup done, including
        closing files.

    INPUTS
        seglist - BCPL pointer to a segment identifier

    RESULTS
        success - returns 0 if a NULL seglist was passed or if it failed
                  to close an overlay file.  NOTE: this function returned
                  a random value before V36!

    SEE ALSO
        loadseg(), internalloadseg(), internalunloadseg()