Trying to test some code in Pharo 2.0 and it depends on BlockContext which was dropped, what can I do?
You can download Pharo 4 and run Magritte 3 and Seaside 3.1, as that are the stable versions. The major change in Magritte 3, introduced and explained early 2012, is the moving of the descriptions to the instance side, and renaming description to magritteDescription. You can find sample code of Seaside & Magritte in a QCMagritte image you can download from CI, in addition to the plain magritte builds
Otherwise, just check the pharo, seaside and pier mailing lists of 4 years ago and the monticello repositories to see what changed. There have been lots of little changes because of the improvements in Squeak and Pharo in the past 4 years.
If you need to use Magritte 2 to migrate legacy code you might want to take a look (with Pharo 5) at my experimental MonticelloProjects code on Smalltalkhub. That builds a data structure of all source code in the Monticello packages in a project repository, allowing you to more easily see what changed when.