Straightforward port of geometrictransform plugin
Rework bulge mapping function to give more predictable results. Now the bulge is done dividing by a scale factor that smoothsteps from "zoom" at the center to 1.0 at "radius". https://bugzilla.gnome.org/show_bug.cgi?id=625908
https://bugzilla.gnome.org/show_bug.cgi?id=625908
Ports gleffects "bulge" filter to geometrictransform. Adds a protuberance around the center point. https://bugzilla.gnome.org/show_bug.cgi?id=625722