Patch tested by compiling with `__attribute__ ((format (printf, 2, 3)))`
applied to `cmd_results_new`.
String usage constants have been converted from pointers to arrays when
encountered. General handler format strings were sometimes modified to
include the old input string, especially for unknown command errors.
Fixes `hide_edge_borders smart` when gaps are in use.
Implements `hide_edge_borders smart_no_gaps` and `smart_borders
on|no_gaps|off`.
Since `smart_borders on` is equivalent to `hide_edge_borders smart`
and `smart_borders no_gaps` is equivalent to `hide_edge_borders
smart_no_gaps`, I opted to just save the last value set for
`hide_edge_borders` and restore that on `smart_borders off`. This
simplifies the conditions for setting the border.
