repl: make invalid RegExp modifiers throw in the REPL

Fixes #4012.

lib/repl.js

@@ -273,6 +273,7 @@ function REPLServer(prompt, stream, eval_, useGlobal, ignoreUndefined) {
       return e && e.match(/^SyntaxError/) &&
              // RegExp syntax error
              !e.match(/^SyntaxError: Invalid regular expression/) &&
+             !e.match(/^SyntaxError: Invalid flags supplied to RegExp constructor/) &&
              // JSON.parse() error
              !(e.match(/^SyntaxError: Unexpected token .*\n/) &&
              e.match(/\n    at Object.parse \(native\)\n/));

test/simple/test-repl.js

@@ -130,6 +130,10 @@ function error_test() {
     // should throw
     { client: client_unix, send: '/(/;',
       expect: /^SyntaxError: Invalid regular expression\:/ },
+    // invalid RegExp modifiers are a special case of syntax error,
+    // should throw (GH-4012)
+    { client: client_unix, send: 'new RegExp("foo", "wrong modifier");',
+      expect: /^SyntaxError: Invalid flags supplied to RegExp constructor/ },
     // Named functions can be used:
     { client: client_unix, send: 'function blah() { return 1; }',
       expect: prompt_unix },