at pairing time, change couchdb pairing address to public

To be as safe a possible, couchdb binds to address 127.0.0.1 . If paired databases on other machines are to talk to it, it must bind to a public address.

In the desktopcouch pairing app, at exit time, check the bind address in the config file, and if its neither 127.0.0.1 or 0.0.0.0, then do nothing. Else, count the number of paired, noncloud machines -- f it is zero, set the bind address to 127.0.0.1; if more than zero, set the bind address to 0.0.0.0 .