Adapt test expectations to V8 error message changes

V8 5.1 uses slightly changed SyntaxError messages.
This adapts our tests as needed (for support of V8 5.1 as well
as older versions)

tests/checkstring.phpt

@@ -20,5 +20,5 @@ Deprecated: Function V8Js::checkString() is deprecated in %s on line %d
 bool(true)
 
 Deprecated: Function V8Js::checkString() is deprecated in %s on line %d
-string(60) "V8Js::checkString():1: SyntaxError: Unexpected token ILLEGAL"
+string(%d) "V8Js::checkString():1: SyntaxError: %s"
 ===EOF===

tests/checkstring_compile.phpt

@@ -17,5 +17,5 @@ try {
 ===EOF===
 --EXPECTF--
 resource(%d) of type (V8Js script)
-string(62) "V8Js::compileString():1: SyntaxError: Unexpected token ILLEGAL"
+string(%d) "V8Js::compileString():1: SyntaxError: %s"
 ===EOF===