[Exim] "$" in filter file

I was having problems a while back with testing for "$" in a subject line.
Upon further R'ing TFM, I discovered that the escape ("\") requirements are
different if the string is surrounded by quotes.

Oops.

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Dennis Taylor
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I sometimes wonder what a battle would be like between the
Enterprise's security team, who are killed almost instantly
after arriving, and Imperial Stormtroopers, who can't hit the
broad side of a planet...
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