need set svn property in commit
my user story: i use mercurial as local svn client. There are two central svn repositories: project and engine
project use engine via svn:external property: engine -r123 http://myserver/engine
I need upgrade project to new engine version. I update engine to new version, fix project code to support changes in engine. Now i need atomic commit project changes and set svn:external to new version.
Commit should be atomic, if it split, project code would be broken, so someone other developer could update to broken version.