Handling of the change log tag in tools/changelog-helper.sh

[pljones]

Quoted mentions of the special "C H A N G E L O G" tag in any comment text in the pull request trigger inclusion of the latest such entry as the change log text.
** This should be amended so only references to the "C H A N G E L O G" tag at the start of a line trigger use (we still need to check the full comment set on the PR)

I've not checked the script code but I expect it's an unbound regexp that can be fixed pretty easily.