Error-aware integration fails with overlapping edits from different authors

[maxg]

Cannot fail; might:

• reject the edit
• make the edit in the original editor's copy only
• share the entire edit between editors

And must work in all cases of additions/deletions that adjoin, overlap, or subsume other additions/deletions.

(Imported from Bitbucket #49 reported by maxg on 2011-06-15)

[maxg]

Addressed by f95a56142086dc8b86d22958d5ce60c10c67418d (maxg on 2011-09-19)