(Qslice): New variable.

(Qslice): New variable.
(syms_of_xdisp): Intern and staticpro it.
(pos_visible_p): Return pixel position in new x and y args.
(init_iterator): Reset it->slice info.
(handle_display_prop): Parse (slice ...) property.
(push_it, pop_it): Save/restore slice info.
(make_cursor_line_fully_visible): Fix 2004-04-14 change.  Do not
force repositioning of tall row if window is vscrolled, as that
would reset vscroll.
(append_space): Set it->constrain_row_ascent_descent_p to avoid
increasing row height if row is non-empty.
(fill_image_glyph_string): Copy slice info.
(take_vertical_position_into_account): Simplify.
(produce_image_glyph): Handle iterator slice info, setup glyph
slice info.  Do not force minimum line height.
(x_produce_glyphs): If it->constrain_row_ascent_descent_p is set,
do not increase height (ascent/descent) of non-empty row when
adding normal character glyph; instead reduce glyph ascent/descent
appropriately; if row is higher than current glyph, adjust glyph
descent/ascent to reposition glyph within the existing row.
Likewise, when char is newline, only set ascent/descent if row is
currently empty.
(note_mouse_highlight): Handle hotspots with sliced image.