Bisect stereo pair into 2 layers

The script is useful to be able to easily compare and edit the two images of a stereo pair in the gimp, by handling the two images as separate layers.

1. This script bisects the two images of a stereo pair to change it into two separate layers.
2. The two layers are piled than by repositioning the right image above the left one
3. the canvas is cropped to the width taken by the two layers (the two stereo pair images) than (cutting the width into halve of the stereo pairs width).

see also http://registry.gimp.org/node/10170, my script to adjoin two separated stereo layers.