Code review comment for lp:~spiv/bzr/better-news-merge

This patch makes the news_merge plugin more capable. Hopefully the changes to comments and docstrings in the patch explain the changes well enough, but in short it makes it capable of coping with conflicts that span section headings (like 'Bug Fixes'), whereas before it only dealt with conflicts between bullet points within a section. See the comments and code for the details (and limitations and tradeoffs).

With this change I expect it news_merge will handle the vast majority of NEWS merges.

A minor orthogonal change adds a couple of trivial mutters to let you a reader of ~/.bzr.log know when news_merge has been used.