image alttext quotes not escaped in info output

[Kevin Ryde]

The file foo.texi below, and an dummy empty foo.png file, processed
with the current cvs makeinfo,

        touch foo.png
        makeinfo foo.texi

produces in the foo.info (full file below),

        [image src="foo.png" alt="This is the "alternate" text.]

But I hoped the " quote marks from the .texi would be escaped in that
blob, the same as they are in "makeinfo --html" on such an input.

foo.texi
Description: TeXInfo document

foo.info
Description: Binary data