Previously, the C function clipmove() returned negative values when hit a
wall (32768+wallnum) or sprite (49152+spritenum) because internally,
these values were encoded into a *signed* 16-bit integer. This made no
difference to C code using it, since it always proceeded by bit checks,
but was inconsistent with documentation on CON 'clipmove' on the wiki.
The following commands are affected too, since they use the value returned
by clipmove(): 'clipmovenoslide', 'movesprite'. Also, the value of
actor[].movflag ('htmovflag' from CON).
Also, fix 'clipmove*' in LunaCON and add lunatic/test/checknearwall.con
as an example of how to implement a being-close-to-a-wall checker as
requested in
http://forums.duke4.net/topic/7869-determining-closeness-to-a-wall/
git-svn-id: https://svn.eduke32.com/eduke32@4874 1a8010ca-5511-0410-912e-c29ae57300e0
