Fix parsing identifiers that start with a non-BMP character

Fixes #498

Author: msimacek

graalpython/com.oracle.graal.python.pegparser/src/com/oracle/graal/python/pegparser/tokenizer/Tokenizer.java

@@ -566,7 +566,7 @@ private static String verifyIdentifier(String tokenString) {
         if (cp != '_' && !UCharacter.hasBinaryProperty(cp, UProperty.XID_START)) {
             invalid = 0;
         }
-        for (int i = 1; i < invalid;) {
+        for (int i = Character.charCount(cp); i < invalid;) {
             cp = tokenString.codePointAt(i);
             if (!UCharacter.hasBinaryProperty(cp, UProperty.XID_CONTINUE)) {
                 invalid = i;