0.9.18.29: --dynamic-space-size command-line switch

0.9.18.29: --dynamic-space-size command-line switch
 * Based on the patch by David Lichteblau. Default size of the
   dynamic space is the same as it used to be, but can be altered
   at startup.
 * Delete dead variables: stop_the_world and
   *INITIAL-DYNAMIC-SPACE-FREE-POINTER*.
 * Rewrote --help output to more typical usage format.