[oe] RFC: Bump default version for gtk+ to 2.18.3

[Rolf Leggewie]

Hi,

as evidenced by http://tinderbox.openembedded.org/packages/407335/ the
current default gtkmm (2.18.1) does not compile with the current default
gtk+ (2.14.2).  My suggestion is to remove DEFAULT_PREFERENCE -1 from
the 2.18.3 recipe and make it the new OE default.

Objections?

Regards

Rolf