Re-introduce sqlapi.host directive, allowing DNS lookups drop

For backward compatibility, sqlapi.host is only used if domain
is also defined and has a different value (empty string allowed).

Closes #117

config/environments/development.js.example

@@ -64,8 +64,15 @@ var config = {
     }
     ,sqlapi: {
         protocol: 'http',
-        domain: 'localhost.lan',
+        // If "host" is given, it will be used
+        // to connect to the SQL-API without a
+        // DNS lookup
+        host: '127.0.0.1',
         port: 8080,
+        // The "domain" part will be appended to 
+        // the cartodb username and passed to
+        // SQL-API requests in the Host HTTP header
+        domain: '',
         version: 'v1'
     }
     ,varnish: {