Commit log messages are not tied to individual files, but to to revisions. A revision may include changes to 1 or more versioned elements.
In other words: There is a 1:1 relationship between log messages and revisions. There is an N:1 relationship between versioned elements and revisions.
Or are you interested in the same commit message being used for multiple revisions? That's a people problem as much as it is a technical one - you really shouldn't have repeated log messages from your committers in most cases. Each one should be descriptive about what is being committed, and it's unlikely that the same change is going to be committed to the same files repeatedly.