(strtox, strtoy): New. Use it instead of inputxy() to avoid the

(strtox, strtoy): New.  Use it instead of inputxy() to avoid the
double-remainder problem: x-coordinate SHRT_MAX+1 is truncated to 0 by
cast to coord, then converted by xabs().  This is wrong unless WORLD_X
divides SHRT_MAX+1.
(sarg_xy, sarg_getrange, sarg_range): Use them.
(inputxy): No longer used, remove.

(sarg_type): Use NS_UNDEF instead of 0.

(sarg_list): Change confusing loop control.  Properly diagnose
overlong lists; used to silently ignore list tail and return MAX+1,
which made a later snxtitem_list() fail.

(atoip): No longer used, remove.  Parsing was broken anyway.

(sarg_type, sarg_xy, sarg_area, sarg_range, sarg_list, sarg_getrange):
Use plain char * instead of s_char *.