Fixed wrong string formatting call

The number of arguments were missing last one. As discussed it's debugging error, so we actually want the arguments to be printed in the error. This commit fixes the formatting error, and adds the list of arguments to be printed together with the error.

Signed-off-by: Jelmer Vernooij <jelmer@samba.org>
Merge branch 'master' of git://github.com/jelmer/dulwich