eqn mishandles quoted strings in macro arguments

[Doug McIlroy]

Eqn does not take quotes into account when parsing macro
arguments. Example:
        .EQ
        define f % $1 %
        f("a,b")
        .EN
Eqn thinks the call of f has two arguments, each with an
unmatched quote. This interpretation violates the plain
meaning of this statement in classic (e.g v7 and v10)
man pages for eqn: `Strings enclosed in double quotes " "
are passed through untouched.' (Full disclosure: v7
eqn did not support macros with arguments; v10 eqn did.)

Doug McIlroy