This patch does:

* Makes submenu indicator arrows point in the direction that the submenu
  will pop up (left or right), rather than always right.

* Makes the submenu offset (the vertical offset of each sucessive submenu)
  a #define'd quantity, instead of magic in the middle.
  Someone should make this be user-customizable via .gtkrc etc.

* Removes hard-coding of submenus cascade right, and #define's it.
  This should also be user settable (i18n issues? tfel-ot-thgir languages
  probably should default to cascade left).

* Minor code clean up (moved an assignment that sometimes gets immediately
  by an 'if ...' into the 'else').