model: Add a comment on the n_columns field type
model: Add a comment on the n_columns field type

To avoid another bug report like:

  http://bugzilla.openedhand.com/show_bug.cgi?id=2017

with a patch that gets applied without a proper review, resulting in a
bug like:

  http://bugzilla.openedhand.com/show_bug.cgi?id=2032

I should probably add a comment on why on earth we're using an integer
as the n_columns member of the ClutterModelPrivate structure, and why it
is important that it is initialized as -1.

heysion/clutter-clone,jigpu/clutter,GNOME/clutter,jigpu/clutter,djdeath/clutter-android,rkudiyarov/clutter_osx,jigpu/clutter,ebassi/clutter,ebassi/clutter,djdeath/clutter-multithreaded,rkudiyarov/clutter_osx,Distrotech/clutter,Distrotech/clutter,djdeath/clutter-multithreaded,heysion/clutter-clone,GNOME/clutter,djdeath/clutter-android,djdeath/clutter,djdeath/clutter-android,GNOME/clutter,dlespiau/clutter,kerrickstaley/clutter-vala,spatulasnout/clutter,spatulasnout/clutter,spatulasnout/clutter,collects/clutter,djdeath/clutter,djdeath/clutter,jigpu/clutter,rkudiyarov/clutter_osx,nobled/clutter,djdeath/clutter-multithreaded,spatulasnout/clutter,nobled/clutter,Distrotech/clutter,rkudiyarov/clutter_osx,kerrickstaley/clutter-vala,djdeath/clutter-android,djdeath/clutter,Distrotech/clutter,nobled/clutter,collects/clutter,ebassi/clutter,heysion/clutter-clone,djdeath/clutter-multithreaded,ebassi/clutter,dlespiau/clutter,spatulasnout/clutter,GNOME/clutter,Distrotech/clutter,kerrickstaley/clutter-vala,collects/clutter,heysion/clutter-clone,jigpu/clutter,heysion/clutter-clone,jigpu/clutter,collects/clutter,djdeath/clutter,GNOME/clutter,Distrotech/clutter,djdeath/clutter-android,kerrickstaley/clutter-vala,ebassi/clutter,dlespiau/clutter,djdeath/clutter,collects/clutter