[idn] quick & dirty (but not too dirty) homograph defense

["Adam M. Costello" <idn.amc+0@nicemice.net.RemoveThisWord>]

Here's an idea for a quick-and-dirty enhancement to existing
applications:  Rather than disable IDNA entirely (which is quick but
too dirty), or flag all IDNs (almost as quick but still too dirty),
just flag all IDNs in .com and .net.  This would be significantly less
damaging to IDN deployment (which could proceed unhindered in the other
TLDs, particularly the ccTLDs), but is still extremely simple and could
be rolled out immediately while more sophisticated heuristics are
developed.

AMC