Show error on JBIG2 images.

src/parser.js

@@ -252,6 +252,9 @@ var Parser = (function ParserClosure() {
       if (name == 'RunLengthDecode') {
         return new RunLengthStream(stream);
       }
+      if (name == 'JBIG2Decode') {
+        error('JBIG2 image format is not currently supprted.');
+      }
       warn('filter "' + name + '" not supported yet');
       return stream;
     }