Xmenu didn't wait for another process to ungrab the poiter or keyboard,
ending up in erroneous behavior.  Now it waits.

You must grab the keyboard after reading the input.

In previous versions, all the previous current visible menus are
unmapped and the new currently visible menus are mapped when the
current visible menu changed. Now, using an algorithm that finds
the lowest common ancestor between current and current_new menus,
only the necessary menus are remapped on the display.

Now the triangle indicating submenus is smaller and better looking.

Using pixmaps rather than drawing directly on windows.

Now lines without labels in the input generate a menu separator.