constants.h is now global for all nPose scripts

slave.lsl is now using constants.h, about 1.5kB already saved
doSync is now a status
doingFaceAnim is now a status
gotFaceAnim is now a status

For some reason, this has seems to have cost 504 bytes.  Some testing
is required.
fixed optimized AvLinkNum()
cleanup
fixed: hud not working and unreachable code in core

slave: DoSeats() has been recomposed
sit() function has been put into sitting.h because both core and slave
use it

Optionally inlining the functionality has been dropped because it
seems to need more memory and the source is cleaner without this
duality.
slave: seatedAvs() replaced with sit(); SetAvatarOffset() rewritten
       and inlined