(sct_pstage, sct_ptime, shp_pstage, shp_ptime, lnd_pstage, lnd_ptime):

(sct_pstage, sct_ptime, shp_pstage, shp_ptime, lnd_pstage, lnd_ptime):
Use `short' instead of `unsigned short'.  With variables, plague stage
and time were stored unsigned and used signed, which worked.  Removal
of variables dropped the conversion to signed, which broke
plague_people() (plague.c rev. 1.6): stage didn't progress correctly
due to catastrophic underflow of time.