Fix an old bug that prevented pattern matching agains values containg tables

The function GF.Grammar.PatternMatch.isInConstantForm returned False for all
tables, causing matchPattern to fail, claiming that "variables occur in" the
term if it contains tables.

This problem is several years old, confirmed present in GF 3.2.10 (Oct 2010).

src/compiler/GF/Grammar/PatternMatch.hs

@@ -77,6 +77,7 @@ tryMatch (p,t) = do
   isInConstantFormt = True -- tested already in matchPattern
   trym p t' =
     case (p,t') of
+--    (_,(x,Typed e ty,y)) -> trym p (x,e,y) -- Add this? /TH 2013-09-05
       (_,(x,Empty,y)) -> trym p (x,K [],y)   -- because "" = [""] = []
       (PW, _) | isInConstantFormt -> return [] -- optimization with wildcard
       (PV x,  _) | isInConstantFormt -> return [(x,t)]
@@ -187,6 +188,9 @@ isInConstantForm trm = case trm of
     K _      -> True
     Empty    -> True
     EInt _   -> True
+    V ty ts  -> isInConstantForm ty && all isInConstantForm ts -- TH 2013-09-05
+--  Typed e t-> isInConstantForm e && isInConstantForm t -- Add this? TH 2013-09-05
+
     _       -> False ---- isInArgVarForm trm
 {- -- unused and suspicuous, see contP in GF.Compile.Compute.Concrete instead
 varsOfPatt :: Patt -> [Ident]