Fix ChangeLog generation in 2.4 branch and re-generate 2011/12/13 ChangeLog.

Previously in r22845, trunk's ChangeLog was generated.

git-svn-id: svn+ssh://svn.gnucash.org/repo/gnucash/branches/2.4@22917 57a11ea4-9604-0410-9ed3-97b8803252fd