git-archive ignores export-ignore

Using git 1.6.4.2, the manual page prophesies that:

    Files and directories with the attribute export-ignore won't be
    added to archive files. See gitattributes(5) for details.

However, various tools seem to be unhappy about this attribute. In
particular, checkout complains about invalid attributes:

    $ cat .gitattributes
    *.py export-subst
    *.html export-subst
    juniperxml.cfg export-ignore

    $ git checkout juniperxml.cfg
    export-ignore is not a valid attribute name: .gitattributes:3

It appears that git-archive doesn't seem to respect the attribute
either. Consider the following example:

    cd /tmp
    mkdir foo
    cd foo
    git init
    touch foo.sh
    echo '*sh' > .gitattributes
    git add foo.sh
    git add .gitattributes
    git commit -m test
    git archive HEAD
    pax_global_header00006660000000000000000000000064113261226070014512gustar00rootroot0000000000000052 comment=202d78e6a44c7f10bee2ad96a3b2adc80fc33468
    .gitattributes000066400000000000000000000000041132612260700137430ustar00rootroot00000000000000*sh
    foo.sh000066400000000000000000000000001132612260700121630ustar00rootroot00000000000000

In addition to whatever bugs there might be in reading and applying the
attributes correctly, it would seem that the man page could be a bit
clearer on how and where to apply the attributes.

Assuming PEBKAC for the moment, how can I get the behavior I'm
expecting?

-- 
"Oh, look: rocks!"
	-- Doctor Who, "Destiny of the Daleks"