This is the acutal sitting avatar crossing code. This commit implements the
actual crossing mechanics for seated avatars, using the supporting code from
the previous commits. Physics is not supported yet, although some few bits
for them are already in place due to the earlier code drops. With this commit,
crossing sitting avatar by "editing" the prim across the border, by using
llSetPos or keyframe motion may already be possible. Vehicles will come next.
Merge branch 'master' of melanie@opensimulator.org:/var/git/opensim