Clearer option in "Amend" to re-use previous commit's comment

The current behavior when "Amend"-ing a commit:

• If the comment dialog is blank and "Amend" is checked, the previous commit's message is automatically populated
• If the comment dialog is not blank and "Amend" is checked, nothing is changed.

For the second bullet point, the usual workaround is to clear the message and uncheck-then-check "Amend".  I realized this while playing around with SmartGit from day 1, but I realize that none of my teammates realize this.

Perhaps add another explicit checkbox like "override with previous commit's message".  Implicit behavior (i.e. having to manually clear the field) is bad UI, IMO.