(lface_equal_p): Compare strings differently.

(lface_equal_p): Compare strings differently.
(Qtty_color_alist, Vtty_defined_color_alist): New variables.
(realize_tty_face): Use them.
(syms_of_xfaces): Initialize new variables.
(map_tty_color): New function, extracted from realize_tty_face.
(map_tty_color) [MSDOS || WINDOWSNT]: If using the frame's default
foreground or background color, store the new color name in the
realized face; previous code trying to do this had no effect.
(realize_tty_face): Use map_tty_color.
(Fclear_face_cache): Set face_change_count and ensure thorough
redisplay.