Honor :fore/background for XBM on NS (Bug#14969).

Honor :fore/background for XBM on NS (Bug#14969).

* nsterm.h (EmacsImage): Add xbm_fg, remove initFromSkipXBM,
initFromXBM takes bg, fg args, remove flip arg.
(ns_image_from_XBM): Add bg, fg args.
* image.c (x_create_bitmap_from_data)
(Create_Pixmap_From_Bitmap_Data): ns_image_from_XBM takes bg, fg args.

* nsimage.m (ns_image_from_XBM): Add fg, bg args, pass to initFromXBM.
Remove flip arg.
(initFromSkipXBM): Move code to initFromXBM.
(initFromXBM): Actually set fg and bg, instead of playing alpha games.
Use fg, bg from args (Bug#14969).  Remove if (length) section, was always
false.
Remove bit flipping (bitPat, swt), generated incorrect images when
width/height wasn't a multiple of 8.
(setXBMColor:): Modify planes by comparing to saved xbm_fg.

* nsterm.m (ns_draw_fringe_bitmap): initFromXBM takes fg, bg args, remove
flip arg.