attribute merges to the branch author, NOT the merger
Modified the script to pick up commits that were NOT introduced through a merge.
(since we do many backports this way)

Cherry-picks are attributed to the picker, though, NOT to the original author.
Make the script more portable
Mimick the reStructuredText format of the previous Changelog
Added debug mode as an option
Corrected the portability issue
Thanks Toni (and the Macbook in the conf' room)
Minor correcitons, as per @dragos comments
Merge pull request #331 from huitseeker/patch-script-to-generate-changelog

Improvements to the ChangeLog script