Better log messages for using external libzmq

This should help when debugging install failures.

Author: lgeiger

scripts/prebuild-install.js

@@ -5,7 +5,7 @@ var platform = process.platform;
 var arch = process.arch;
 
 if (process.env.npm_config_zmq_external == "true") {
-  /* Requested to use external libzmq, we must rebuild. */
+  console.log('Requested to use external libzmq. Skipping download of prebuilt binaries.');
   process.exit(1);
 }
 

scripts/preinstall.js

@@ -7,7 +7,7 @@ var ZMQ = "4.2.2";
 var ZMQ_REPO = "libzmq";
 
 if (process.env.npm_config_zmq_external == "true") {
-  console.log("Skipping libzmq build");
+  console.log("Requested to use external libzmq. Skipping libzmq build");
   process.exit(0);
 }