Major improvement to the Xconq kernel

[Hans Ronne]

>> * One SIGSEGV.  Most interesting part of the stack trace follows.
>>   Because the default compilation uses -O, it is hard to quickly
>>   look at the variables at that point.
>>
>> #5  0x080af4da in point_in_dir (x=6, y=0, dir=135856599, xp=0xbfffde44,
>>yp=0x0)
>>     at world.c:1459
>> #6  0x08076069 in attack_blockage (side=0x8381a98, unit=0x8189dcc,
>>     dirp1=1108574732) at ai.c:2483
>> #7  0x0807144b in ai_react_to_task_result (side=0x6, unit=0x8189dcc,
>>     task=0x8416394, rslt=TASK_FAILED) at ai.c:553
>
>The y=0 looks highly suspicious.

Indeed. I've had problems with point_in_dir before at the map edge.

>I have gone through
>all the code I submitted and identified areas where I could be ignoring
>the boundary and added extra assertion checks. I dont think
>any of it is too onerous for production code.
>
>Here is the patch.

I'll check it in. I don't have much time for more testing right now, but
hopefully others could have a go at it.

Hans