0.6.0-beta - prerelease of the core rework

This is the first release after the rework of the crabgrass codebase.
Some years ago the crabgrass codebase had diverged into different
incompatible development trees. We're about to bring the different forks
back together in a streamlined version.

The 0.6 series was migrated to rails 3.2 and ruby 1.9.3.

This beta release is mostly stable. The bugtracker lists 36 open bugs
for 0.6.0.