show commandline and/or rev info in diff output

Here is bzr diff output:

    === added file 'Makefile'
    --- Makefile 1970-01-01 00:00:00 +0000
    +++ Makefile 2007-08-05 21:38:10 +0000

I propose that an indentification like is added to the beginning of
diff to announce who generated the output. The command and options
could be added verbatim:

    bzr -r1..3 Makefile (bzr v0.18)
    === added file 'Makefile'
    --- Makefile 1970-01-01 00:00:00 +0000
    +++ Makefile 2007-08-05 21:38:10 +0000

I assume here that patch(1) will skip over the added 1st line.

FURTHER DETAILS

    I use a tool that deal with various version control sources and
    sometimes there is need to detect from which source certain patch
    comes from. E.g. Mercurial uses extra pseudo directories in output:

        --- a/Makefile.in Sun Aug 05 20:45:37 2007 +0300
        +++ b/Makefile.in Sun Aug 05 23:55:17 2007 +0300

    For a tool, it is most difficult to tell if "a/" is genuine directory
    or not and if --strip option would be needed or not during patching.

    [Martin Pool]

    Some diff tools prefix the diff with the command that generated
    it, or a cleaned-up version of the command. If we included that it
    would both indicate that it came from bazaar and maybe give some
    other useful information

    Otherwise this seems ok, as long as it's tested and optional.

    http://permalink.gmane.org/gmane.comp.version-control.bazaar-ng.general/29033