prepare-Changelog.pl for git

[Matthieu Herrb]

Donnie Berkholz wrote:
> Donnie Berkholz wrote:
>> Whenever you commit to a repo, please double-check whether there's a
>> Makefile.am rule to generate the ChangeLog on `make dist`. If not,
>> delete the ChangeLog and copy the rule over from libX11.
> 
> BTW, I just added another fix to this rule courtesy of Aaron Plattner,
> so make sure you pull the latest stuff before copying it.
> 

The rule used in many commited Makefile.am doesn't work if building with 
builddir != srcdir. I'd suggest to use:

ChangeLog:
	GIT_DIR=${srcdir}/.git git-log > ChangeLog

instead.
-- 
Matthieu Herrb