Include _connect in ignore_exc try/except block

The Best Practices section of the docstring explicitly suggests [using `ignore_exc` to make network errors look like misses](https://github.com/pinterest/pymemcache/blob/master/pymemcache/client.py#L63-L67) but if the client is new and not connected, [the `_connect` call](https://github.com/pinterest/pymemcache/blob/master/pymemcache/client.py#L63-L67) is not wrapped in a try/except block.

I assume this is an error in the client and not the docs.