Fix calls to dns bindings in dns.js

lib/dns.js

@@ -1,4 +1,4 @@
-process.binding('dns');
+var dns = process.binding('dns');
 
 exports.resolve = function (domain, type_, callback_) {
   var type, callback;
@@ -19,32 +19,32 @@ exports.resolve = function (domain, type_, callback_) {
   }
 }
 
-exports.resolve4    = process.dns.resolve4;
-exports.resolve6    = process.dns.resolve6;
-exports.resolveMx   = process.dns.resolveMx;
-exports.resolveTxt  = process.dns.resolveTxt;
-exports.resolveSrv  = process.dns.resolveSrv;
-exports.reverse     = process.dns.reverse;
+exports.resolve4    = dns.resolve4;
+exports.resolve6    = dns.resolve6;
+exports.resolveMx   = dns.resolveMx;
+exports.resolveTxt  = dns.resolveTxt;
+exports.resolveSrv  = dns.resolveSrv;
+exports.reverse     = dns.reverse;
 
 // ERROR CODES
 
 // timeout, SERVFAIL or similar.
-exports.TEMPFAIL = process.dns.TEMPFAIL;
+exports.TEMPFAIL = dns.TEMPFAIL;
 
 // got garbled reply.
-exports.PROTOCOL = process.dns.PROTOCOL;
+exports.PROTOCOL = dns.PROTOCOL;
 
 // domain does not exists.
-exports.NXDOMAIN = process.dns.NXDOMAIN;
+exports.NXDOMAIN = dns.NXDOMAIN;
 
 // domain exists but no data of reqd type.
-exports.NODATA = process.dns.NODATA;
+exports.NODATA = dns.NODATA;
 
 // out of memory while processing.
-exports.NOMEM = process.dns.NOMEM;
+exports.NOMEM = dns.NOMEM;
 
 // the query is malformed.
-exports.BADQUERY = process.dns.BADQUERY;
+exports.BADQUERY = dns.BADQUERY;
 
 var resolveMap = {
   'A': exports.resolve4,