With this change, units will not check their movement against all
obstructions when moving: terrain and static obstructions are assumed to
be handled by the long-range pathfinder.
However, when static obstructions are changed, the paths have to be
invalidated. In order to minimize the performance impact, units will
check for obstructions when they move after a passability change. If
they collide with something, they will recompute a path that will take
into account the new passability map.
Also includes some code cleanup. This patch should not change
performance a lot: the lower number of checks should give a small
performance improvement while using the message broadcasting system
should hurt it a bit.
Fixes#3376, #3337, #1914.
This was SVN commit r16998.