This patch allows ZipFile.writestr() to be called with
an archive file name instead of a ZipInfo instance:

    z = ZipFile("myarchive.zip", "w")
    z.writestr("foo/baz/file.ext", data)
    z.close()

I find the current writestr() method very inconvenient
for simple (but common) things.

If called with a file name instead of a ZipInfo
instance, the date_time is set to now, which makes most
sense for anonymous data.

The patch also patches Doc/Lib/libzipfile.tex.

Just