No more DANE lookups for internal handler pages

[techhazard]

The proxy used to try and connect to some internal addresses (but not
others)

This makes it explicit that the eccaProxy function will handle
everything but "ecca.handler" requests which will result in no more
DANE lookups for internal pages which, in turn, will result in no more
errors in the log about unavailable DANE records.

[gwitmond]

Regrettable, in my environment, this gives a worse error than the missing dane record you want to avoid. To reproduce: install this PR, close your browser, reopen and navigate to ecca.handler/manage. Boom.

2017/03/11 21:21:17 http: panic serving 127.0.0.1:41281: runtime error: invalid memory address or nil pointer dereference
goroutine 12 [running]:
net/http.(*conn).serve.func1(0xc8203ba800)
        /usr/lib/go-1.6/src/net/http/server.go:1389 +0xc1
panic(0x9567e0, 0xc82000e140)
        /usr/lib/go-1.6/src/runtime/panic.go:443 +0x4e9
main.DecodeMessages(0x0, 0xc820359cc0, 0x422201)
        /home/guido/gopath/src/github.com/gwitmond/ecca-proxy/proxy.go:457 +0x45

[techhazard]

I see, I'll look into another way of mitigating this.

[techhazard]

Would you still like to merge this? Because then I'll look into it.
Otherwise I'll close this