pg_dump docs: use escaped double-quotes, for Windows

On Unix, you can embed double-quotes in single-quotes, and via versa.
However, on Windows, you can only escape double-quotes in double-quotes,
so use that in the pg_dump -t/table example.
Backpatch to 9.3.
Report from Mike Toews

doc/src/sgml/ref/pg_dump.sgml

@@ -1224,7 +1224,7 @@ CREATE DATABASE foo WITH TEMPLATE template0;
    like
 
 <screen>
-<prompt>$</prompt> <userinput>pg_dump -t '"MixedCaseName"' mydb &gt; mytab.sql</userinput>
+<prompt>$</prompt> <userinput>pg_dump -t "\"MixedCaseName\"" mydb &gt; mytab.sql</userinput>
 </screen></para>
 
  </refsect1>