Use first line of commit message in commit list (BB-2182)

It is usual in web interfaces for DVCS's that the first line in any commit message is shown in the web interface, so that the developer can give a brief summary and then a detailed message later. This is the case in the normal "grey/white" hg web interface, as it is in Github and Gitorious. In Bitbucket, however, the other lines are just tacked onto the end, even if there are two newlines between them, as there always are in my commit messages. This should be corrected.