Tell hg-git to be backwards compatible

Since version 0.7.0 hg-git stores extra information directly into the
commits, we don't support that, so we need to tell hg-git to do what it
always did: put the extra data in the message.

Signed-off-by: Felipe Contreras <felipe.contreras@gmail.com>

test/hg-git.t

@@ -108,6 +108,8 @@ setup () {
 	[extensions]
 	$hggit =
 	graphlog =
+	[git]
+	debugextrainmessage = 1
 	EOF
 	git config --global receive.denycurrentbranch warn
 	git config --global remote-hg.hg-git-compat true