tests: also allow "Protocol not supported" in test-http-proxy error

I've seen this in a (misconfigured) FreeBSD jail which has ::1 as an
entry for localhost, but IPv6 support is disabled in the jail. It took
me months to figure out what was going on (and I only figured it out
when tinyproxy.py got confused by similar IPv4-level misconfiguration
of the localhost domain in /etc/hosts.)

I don't feel strongly about this patch: on the one hand, it's papering
over a host-level misconfiguration, but on the other it avoids some
weird and hard to diagnose problems that can occur in weirdly
restricted environments.

tests/test-http-proxy.t

@@ -83,10 +83,11 b' url with user name and password'
   updating to branch default
   1 files updated, 0 files merged, 0 files removed, 0 files unresolved
 
-bad host:port for proxy
+bad host:port for proxy ("Protocol not supported" can happen on
+misconfigured hosts)
 
   $ http_proxy=localhost:$HGPORT2 hg clone --config http_proxy.always=True http://localhost:$HGPORT/ f
-  abort: error: Connection refused
+  abort: error: (Connection refused|Protocol not supported) (re)
   [255]
 
 do not use the proxy if it is in the no list