[PATCH] Add commit message guidelines to developer policy

[hfinkel at anl.gov]

In http://reviews.llvm.org/D8197#141159, @shankarke wrote:

> - What is the commit message policy when reverting a change ?


There seem to be two important issues that have come up repeatedly that are likely worth mentioning:

1. Include a rationale.
2. Include the svn revision number(s) [and, specifically, not the git-svn hash ids]


http://reviews.llvm.org/D8197

EMAIL PREFERENCES
  http://reviews.llvm.org/settings/panel/emailpreferences/