(display_tool_bar_line): Skip glyphs which are too big

(display_tool_bar_line): Skip glyphs which are too big
to ever fit the tool-bar,
(MAX_FRAME_TOOL_BAR_HEIGHT): New macro.
(tool_bar_lines_needed): Use unused mode-line row as temp_row.
(redisplay_tool_bar): Only clear desired matrix if we actually
change the tool-bar window height.  Only try to make the tool-bar
window bigger if there is actually room for it.