Generate ChangeLog from git log during 'make dist'

Generate ChangeLog from git log during 'make dist'

Generate the ChangeLog using git log in the dist-hook target of the main
Makefile.  The git command used is:

	git log --stat --name-only --date=iso

The format of the resulting ChangeLog is different to the old one that
was produced with cvs2cl.

Signed-off-by: Ian Abbott <abbotti@mev.co.uk>