Invert characters' rendering when text cursor is fat

[Masatake YAMATO <jet gyve org>]

Could you review my patch and install it if you appreciate?
      
      http://bugzilla.gnome.org/show_bug.cgi?id=347373

I'm using following gtkrc to make the text cursor more strongly rendered:

  style "default"
  {
     GtkWidget::cursor-aspect-ratio = 1.0
  }
  class "GtkWidget" style "default"
  gtk-cursor-blink = 0

However, this setting is not useful: the characters under the cursor
is hidden by the fat cursor itself. The fat cursor may be one of general
requirements from shortsighted users.

With my patch in the bugzilla entry, the characters under the cursor is
rendered with the color different from the cursor's color(like emacs).

Regards,
Masatake YAMATO