SeaMonkey 2.6 Beta 2

# SeaMonkey-specific changes:
- Added support for the HTML5 "context menu" feature (contextmenu attribute)
- Added Print Preview support to Composer
- Added update channel indication to About SeaMonkey page (about:)

# Mozilla platform changes:
- Added Type Inference, significantly improving JavaScript performance
- Added support for querying Do Not Track status via JavaScript
- Added support for font-stretch
- Improved support for text-overflow
- Improved standards support for HTML5, MathML, and CSS
- Fixed several stability issues