scribble: render "incremement" and some other chars for Latex/PDF

This change was prompted by the change to DrRacket's "\Delta"
to produce the Unicode "increment" character.

collects/mrlib/tex-table.rkt

@@ -92,7 +92,7 @@
     ("Lambda" "Λ")
     ("Sigma" "Σ")
     ("Psi" "Ψ")
-    ("Delta" "Δ")
+    ("Delta" "Δ") ; <- this character is Unicode "increment", not Greek delta
     ("Xi" "Ξ")
     ("Upsilon" "Υ")
     ("Omega" "Ω")

collects/scribble/latex-render.rkt

@@ -853,6 +853,12 @@
                             [(#\♭) "$\\flat$"]
                             [(#\♮) "$\\natural$"]
                             [(#\√) "$\\surd$"]
+                            [(#\Δ) "$\\Delta$"] ; no better mapping for than \Delta for "increment"
+                            [(#\u2211) "$\\sum$"] ; better than \Sigma, right?
+                            [(#\u220F) "$\\prod$"] ; better than \Pi, right?
+                            [(#\u2210) "$\\coprod$"]
+                            [(#\u222B) "$\\int$"]
+                            [(#\u222E) "$\\oint$"]
                             [(#\¬) "$\\neg$"]
                             [(#\△) "$\\triangle$"]
                             [(#\∀) "$\\forall$"]