(dchrstr): Replace int members d_mcst and d_emcst (mobility cost * 5)

(dchrstr): Replace int members d_mcst and d_emcst (mobility cost * 5)
by float d_mob0 and d_mob1 (straight costs).  Impassable terrain now
encoded as negative d_mob0 instead of zero d_mcst.  Users changed.
sect.config updated.
(dchr_ca): Replace selectors mcst and emcst by mob0 and mob1.
(show_sect_stats): Show real mobility costs.