GIMP 2.8 Python Plug-in.
This plug-in scales the contents of the layer (or layer group) to image size.

Installation:
1. Close GIMP if it is open.
2. Extract "scale-layer-to-image-size.py" from zip archive to the ".../.gimp-2.8/plug-ins" directory.
3. Run GIMP. The plug-in should appear under the menu: "Layer > Scale Layer to Image Size". Don't forget to make the plug-in executable.

Download:
Download from my deviantart page:
slybug.deviantart.com

Tested with GIMP 2.8.
I hope this plug-in will be useful for someone else.

Version History:
v1.3 (01.06.2012)
- Added support for working with layer groups.
- To the two types of scaling added three more.
- Added "Align to image center" option.
- Fixed bug in "Crop to Image Size" which leads to cropping of the whole image, and not the selected layer.
v1.2 (19.05.2012)
- Added "Crop to Image Size" option.
- The value "Addition" is now measured as a percentage (%).
- Some code improvements.
v1.0 (13.05.2012)
- Initial release.

My other plugins:
Create Layer Mask from...
Duplicate to another Image
Layer via Copy/Cut

I guess it doesn't work in gimp-2.6.12. I downloaded and added it to my plug-in folder. It shows under layers but when I click it no dialog comes up. Do I have to have more than one layer or make a selection?

Something I could have done with a number of times. When my internet connection is running a bit faster I'll download this one. Thank you.

Sorry, this script most probably does not work in gimp-2.6.12. You may have few layers in a composition, but the script can be applied only to the selected layer.

The reason is that you use pdb.gimp_context_set_interpolation() which is new in 2.8.

IMHO this isn't really useful... There is a default interpolation that you can use.

thank you guys

v1.3 (01.06.2012)
Added support for working with layer groups.

Thanks Slybug.

You are welcome Rod