The checksum file has been updated and uploaded with the July google updates (for Nexus and Google devices) for full fastboot images and OTA images (flashable through stock recovery). This file takes a checksum of any google firmware image flashed through the Toolkit to make sure the download was complete and the file is good before flashing. All Toolkits will download the new file for use after device selection.
I am downloading the new firmware images now for the July google updates and will start pushing support in the next 2 days.
If you want to donate to a device project to enable the latest updates please do it through the Toolkit (after selecting the device at startup) or from the link at http://www.skipsoft.net/?page_id=703 so you get the right code fast. Also follow me on twitter at https://twitter.com/mskipxda for posts/updates.