FIX: devtools message manager is null on "remote=true" iframe

I'm not sure if this is a problem of my development environment, but I have to set the *remote* attribute to *false* on the frame node element to get the *debug-client* example to work:

If remote is true, frame.frameLoader.messageManager returns a null object.

tested on Ubuntu Linux 13.04:
- Firefox 29.0
- Firefox 31.0a2
- Firefox 32.0a1 (2014-05-04)