problem with vc-annotate using git 1.5.6

[Bob Rogers]

   vc-annotate of (e.g.) sql.el does not work for me under git because
emacs runs the equivalent of:

        git blame --date=iso -C -C master sql.el

and gets this error:

        fatal: cannot stat path lisp/progmodes/master: No such file or directory

This seems to be because "master" is passed as the "rev" arg to
vc-git-annotate-command, but git interprets this as a file rather than a
revision.  Is this perhaps a compatibility problem with the version of
git I am using?  TIA,

                                        -- Bob Rogers
                                           http://www.rgrjr.com/