Prevent .onmatch from being called if an assertion is generated in the dialog.

@lloyd - I would love to pow-wow on this. My "fix" is any time an assertion is generated by the dialog, do not then attempt to generate an assertion in the communication_iframe.

I am not convinced this is correct, but the behavior has survived IE8 with every combination of primary/secondary, single or multiple browsers that I could think of.

issue #3170