Fix minor problems found by static checking.

Fix minor problems found by static checking.

* image.c (XGetPixel, XPutPixel) [HAVE_NS]: Now static.
(expect): Avoid nested-if warning.
(x_build_heuristic_mask) [HAVE_NS]: Avoid unused-var warning.
* nsmenu.m (fillWithWidgetValue:): Avoid type warning.
* nsterm.h, nsterm.m (ns_select):
* xgselect.c, xgselect.h (xg_select):
Adjust signature to better match pselect's.
* nsterm.m (ns_select):
Don't set *TIMEOUT, since pselect doesn't.
* regex.c (whitespace_regexp): Now const_re_char *, to avoid
diagnostic about assigning const char * to it.
* xfaces.c (x_display_info) [HAVE_NS]: Remove; unused.