to examples/.

+ Added -Wsign-compare to the warning flags.
  * libcaca/caca.c:
    + Fixed a signed/unsigned bug that caused infinite waits with
      ee_set_delay(0).
  * src/weapons.c libcaca/graphics.c libcaca/blit.c libcaca/conic.c:
    + Fixed minor signed/unsigned comparison warnings.

+ Added a note about dos cross-compilation.
  * configure.ac:
    + Added a check for ScreenUpdate in <pc.h>.
  * libee/graphics.c libee/ee.c:
    + Improved the conio port thanks to ScreenUpdate().

+ Moved optimization flags and warning triggers here.
    + Updated the snapshot timestamp.

+ Wrote a little sprite demo.
  * data/:
    + Added bar_fighter (from ttyvaders) and bar_boss (from shapes.txt).

* replaced '�' with ':' in the fragbomb tail because it's not ASCII.

* lots of sanity checks in collide.c.
  * moved usleep() to graphics.c.
  * added random key generator in the dummy driver.
  * cosmetic changes in the energy bars.

* fixed an overflow in the tunnel update code.
  * fragbomb is now 'f', not 'd'.
  * added a missing call to init_bonus().

* two new types of aliens. only one rules.
  * removed gfx_write in favor of gfx_putchar and gfx_putstr.
  * added bonuses at alien death. they do nothing yet.
  * seeker missiles. 'b' to test.
  * weapon resolution is now 16*char. needs to be generalized.
  * fixed the supernova bugs. center could collide with the tunnel, and
    the last frame was badly displayed.
  * lots of cleanups everywhere.