In branch "feature/temporary" it is currently not possible to go back to a specific layout version.
Steps to reproduce:
Install standard client with content.
Go to Style -> Layouts -> standard
Edit Layout and click save buttton
Click on history for standard layout
Select a revision or just push the save button.
Internal server error comes up.
File errorlog.txt contains the following entry:
[27-Feb-2015 15:21:39 UTC] PHP Fatal error: Call to undefined function layEditLayout() in C:\projects\workspace\con_git\contenido\includes\include.lay_history.php on line 55
Research what happened to this function and fix the problem.