Incursion stabilisation post 2

Suck-cess!  There's some problem with foreground and background colour not taking, but that's a minor detail.  Incursion is now basically playable with a libtcod backend.

Incursion stabilisation post 1

I've been working on replacing the use of Allegro in Incursion, as it only works in the Debug build.

Unfortunately, most of last night and today was spent trying to work out why at first calloc() was failing, returning NULL with an errno of 12 (NOMEM).  Luckily, after an eventual reboot that switched to the call to TCOD_console_set_custom_font() crashing on exit.

Finally, I noticed that I was passing 8 and 8 respectively, as my font's nb_char_horiz and nb_char_vertic values.  After correcting it, my code is now stable.  I debugged that function umpteen times, and am not sure how this makes that much of a difference.