The function working_head_info() fails to parse commit hashes if they
are decorated (i.e. log.decorate is true), causing dcommit, rebase, and
other vital git-svn commands to malfunction.
This patch disables decorated log output with --no-decorate.
[ew: wrapped long line]
Signed-off-by: Mathias Lafeldt <misfire@debugon.org> Acked-by: Eric Wong <normalperson@yhbt.net>