design/tpl (\equivish): Symbol change

This uses the same variable subscript on \equiv itself to define the symbol,
rather than the previous symbol which looked like equiv rotated, but also
looked too much like a turnstile used for "infer", a metalanguage construct
that is not appropriate here.  It kept bothering me.

design/tpl/tpl.sty

@@ -119,7 +119,7 @@
 
 % Equivalent, but some syntatic inference involved (e.g. equivalent by
 % index, as in classification matches).
-\newcommand\equivish{\Vvdash}
+\newcommand\equivish{\equiv_{\varsubscript}}
 
 % Group theory
 \newcommand\Monoid[3]{\left({#1},{#2},{#3}\right)}