Grab Viewport (with alpha channel)

The script that grab the active viewport and include an alpha channel was requested in cgtalk forum.

So, this is my attempt. Note that the script is not very fast. Test it and if you like it - use it. :)

ver.1.1 - can take a screenshot that's larger than the viewport resolution. - idea by Bigjohn

ver.1.2 - the year, month, day, hour,minutes, seconds will be added as a suffux to the name of the created iamge.