(x_produce_stretch_glyph): Only use Qspace when GLYPH_DEBUG is defined.

(x_produce_stretch_glyph): Only use Qspace when	GLYPH_DEBUG is defined.
(x_produce_glyphs): Don't xassert `it->descent > 0'; this isn't
true for images with `:ascent 100'.
(x_set_mouse_face_gc): If the last used mouse face has gone in the
meantime, use face MOUSE_FACE_ID.
If first glyph isn't a character glyph, use the ASCII NUL
character to determine the face.
(expose_area): Do not treat left margin specially.
(note_mode_line_highlight): If no local_map, check global keymap.
(note_mouse_highlight): Initialize overlay.
(clear_mouse_face): Don't return if tip_frame is non-nil.
(show_scroll_bars): Remove unused function.
(w32_read_socket) [WM_KILLFOCUS]: Set help_echo to Qnil.
(x_draw_bar_cursor): Remove extra test for out of bounds cursor.
Clip to row.
(x_erase_phys_cursor): Don't apply XWINDOW to variable that may be nil.
(x_free_frame_resources): Unload relief colors.