* gdb.t03/ptype.exp: tests for return code from gdb_test.

   * gdb.t03/ptype.exp: tests for return code from gdb_test.
       * gdb.t00/teststrategy.exp: Uses which proc rather than spawning
       which in a shell. Deletes xgdb when done.
       * config/unix-gdb.exp: Won't try to spawn $GDB unless it exists.
       Tests the return from the "set height" or "set width" commands.
       Added a few return codes where needed.