Collision detection

[csmith]

The edit form should write out a hash of the contents in a hidden field, and if that doesn't match the latest contents on submit the user should be asked if they want to force the change or not.

[ShaneMcC]

This could be done nicely with git in most cases?

Do the edit in a branch, merge/rebase it in, delete the branch?

If it fails to merge, throw an error and show the clashes or so?