Skip regenerating unchanged module dev-releases

[Htbaa]

Currently if a multi-module repository gets updated all dev-releases for all modules are regenerated. This generates quite a lot of load and database I/O. Should add a mechanism that prevents updating dev-releases that haven't actually changed yet.

Perhaps content checksums?

[Htbaa]

Could also generate a diff on the previous and new revision. Then filter out the module names from the output, and only update those modules.