Compile example grammars during the build phase instead of the install phase

This allows more errors to be detected by the build bot.
TODO: fix the gf --output-dir flag, which does not seem to change where PGF
file are put.

Setup.hs

@@ -24,7 +24,7 @@ tryIOE = E.try
 
 main :: IO ()
 main = defaultMainWithHooks simpleUserHooks{ preBuild =gfPreBuild
-                                           , postBuild=buildRGL
+                                           , postBuild=gfPostBuild
                                            , preInst  =gfPreInst
                                            , postInst =gfPostInst
                                            , preCopy  =const . checkRGLArgs
@@ -41,6 +41,11 @@ main = defaultMainWithHooks simpleUserHooks{ preBuild =gfPreBuild
          extractDarcsVersion distFlag
          return h
 
+    gfPostBuild args flags pkg lbi =
+      do buildRGL args flags pkg lbi
+         let gf = default_gf pkg lbi
+         buildWeb gf args flags pkg lbi
+
     gfPostInst args flags pkg lbi =
       do installRGL args flags pkg lbi
          let gf = default_gf pkg lbi