fix rendering of underscores

pkgs/redex-pkgs/redex-pict-lib/redex/private/core-layout.rkt

@@ -708,6 +708,7 @@
                                                pink-code-font
                                                (default-font-size)))))]
       [(and (symbol? atom)
+            (not (equal? atom '_))
             (regexp-match #rx"^([^_^]*)_([^^]*)\\^?(.*)$" (symbol->string atom)))
        =>
        (match-lambda

pkgs/redex-pkgs/redex-test/redex/tests/bitmap-test.rkt

@@ -121,11 +121,12 @@
   [(T x x) 
    (any_1 any_2)
    (where any_1 2)
-   (where any_2 2)])
+   (where any_2 2)]
+  [(T _ _ _) 1234])
 
-;; in this test, the metafunction has 2 clauses 
+;; in this test, the metafunction has 3 clauses 
 ;; with a side-condition on the first clause
-;; and a 'where' in the second clause
+;; a 'where' in the second clause, and an underscore
 (btest (parameterize ([metafunction-cases '("first-one" 1)])
          (render-metafunction T))
        "metafunction-T.png")
@@ -425,5 +426,4 @@
           (render-judgment-form typeof))
          "stlc.png"))  
 
-(printf "bitmap-test.rkt: ")
 (done)