lib: fix TypeError with EventEmitter#on() abuse

Commit 29313483 added EventEmitter#getMaxListeners() but introduced a
regression when people abuse EventEmitter.prototype.on.call() to call
EventEmitter#on() on a non-EE object.  Add a workaround for that.

Fixes: https://github.com/iojs/io.js/issues/523
PR-URL: https://github.com/iojs/io.js/pull/527


Reviewed-By: Colin Ihrig <cjihrig@gmail.com>