Greenlet: when printing the function name and the argument, limit all reprs to 50 chars

gevent/greenlet.py

@@ -191,7 +191,7 @@ class Greenlet(greenlet):
             if self.args:
                 args = [repr(x)[:50] for x in self.args]
             if self.kwargs:
-                args.extend(['%s=%r' % x for x in self.kwargs.items()])
+                args.extend(['%s=%s' % (key, repr(value)[:50]) for (key, value) in self.kwargs.items()])
             if args:
                 result += '(' + ', '.join(args) + ')'
             # it is important to save the result here, because once the greenlet exits '_run' attribute will be removed