Add new semantic analyzer to mypy tests (#3037)

This also removes two redundant definitions in curses/__init__.pyi star-imported from _curses.

tests/mypy_test.py

@@ -21,6 +21,7 @@ parser = argparse.ArgumentParser(description="Test runner for typeshed. "
                                              "Patterns are unanchored regexps on the full path.")
 parser.add_argument('-v', '--verbose', action='count', default=0, help="More output")
 parser.add_argument('-n', '--dry-run', action='store_true', help="Don't actually run mypy")
+parser.add_argument('-a', '--new-analyzer', action='store_true', help="Use new mypy semantic analyzer")
 parser.add_argument('-x', '--exclude', type=str, nargs='*', help="Exclude pattern")
 parser.add_argument('-p', '--python-version', type=str, nargs='*',
                     help="These versions only (major[.minor])")
@@ -132,6 +133,8 @@ def main():
             flags.append('--no-site-packages')
             flags.append('--show-traceback')
             flags.append('--no-implicit-optional')
+            if args.new_analyzer:
+                flags.append('--new-semantic-analyzer')
             if args.warn_unused_ignores:
                 flags.append('--warn-unused-ignores')
             sys.argv = ['mypy'] + flags + files