Make RegExp objects not callable.

test/mjsunit/regexp-call-as-function.js

 // Copyright 2009 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 15 matching lines @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
 // Test that regular expressions can be called as functions.  Calling
 // a regular expression as a function corresponds to calling it's exec
 // method.
 
 var regexp = /a(b)(c)/;
 var subject = "xyzabcde";
 var expected = 'abc,b,c';
 assertEquals(expected, String(regexp.exec(subject)));
-assertEquals(expected, String(regexp(subject)));
+assertThrows(function(){ regexp(subject); });