Paint.NET 2.64

This small updates fixes a few minor bugs, and improves Windows Vista compatibility. As a bonus, it also adds much better GIF save quality.

* Improved GIF save quality by implementing Floyd-Steinburg error diffusion algorithm
* Printing now works in Windows Vista
* Fixed a startup performance problem on some systems that was an artifact of the way the .NET Framework was verifying Authenticode signatures as part of its assembly loading process
* Executable files now have UAC manifests to ensure proper execution privilege and to disable file and registry virtualization in Windows Vista