Auto-generate the ChangeLog from the git log for 'make dist'.

	* Makefile.am: Include the dist-changelog.am file copied in build/
	from mm-common so that the ChangeLog is automatically generated from
	the git commit messages on 'make dist'.
Move to a generated ChangeLog.
Merge branch 'master' of git://git.gnome.org/libsigc++2