Resize the image to 72dpi using /usr/bin/awk and /usr/bin/sips on macs with a Retina display.

With this patch, the captured images are resized on macs with a Retina display before they are uploaded to the remote site.

You can view the standalone version (without escapes for objective-C string literal) of the embedded shell script at:
https://gist.github.com/hnakamur/5284309

Could you review this pull request?
Thanks