bug#3642: mode line menus don't have tool-tips

[jidanni]

The mode line menus don't have tool-tips
E.g., we read in (info "(emacs) VC Mode Line")

     On a graphical display, you can move the mouse over this mode line
  indicator to pop up a "tool-tip", which displays a more verbose
  description of the version control status.

Yes, I see that one.

  Pressing `Mouse-1' over the
  indicator pops up a menu of VC commands.  This menu is identical to the
  `Tools / Version Control' menu item.

Identical, but without any further tool-tips.

In GNU Emacs 23.0.94.1 (i486-pc-linux-gnu, GTK+ Version 2.16.2)