[spaqrl mode] Fix parsing of veriables after operators

Question-mark characters should only be styled as operators within triple patterns. For example the command

SELECT * WHERE { BIND(?A+?B AS ?C) }

should not have the "+?" sequence styled as "operator".  NB the problem does not occur if there is a space between these two characters.
With the fix "?A" and "?B" will both be styled as variable-2 (and "+" as operator).

By processing operators characters (mostly) one at a time,  the existing code on line 40 to zealously interpret anything beginning with '?' as a variable can run in this case. 

NB Line 40 actually causes a false positive in the case where the '?' appears in a triple pattern as a property path operator: this fix does not address this existing bug: it is quite complicated as '?' can appear in both variables and property paths while the parser is in the "pattern" state.

mode/sparql/sparql.js

@@ -60,14 +60,7 @@ CodeMirror.defineMode("sparql", function(config) {
       stream.skipToEnd();
       return "comment";
     }
-    else if (ch === "^") {
-      ch = stream.peek();
-      if (ch === "^") stream.eat("^");
-      else stream.eatWhile(operatorChars);
-      return "operator";
-    }
     else if (operatorChars.test(ch)) {
-      stream.eatWhile(operatorChars);
       return "operator";
     }
     else if (ch == ":") {