Send 'error' log messages to stderr.

lib/selleck.js

@@ -284,10 +284,21 @@ function isProjectDirectory(dir) {
 exports.isProjectDirectory = isProjectDirectory;
 
 /**
-@method log
+Logs a message to stdout or stderr, with an optional log level.
+
+@method log 
+@param {String} message A message to write to the console.
+@param {String} [level] A short string describing the type of message. 
+    If the level is 'error', Selleck logs the message to stderr. 
+    Otherwise, Selleck logs the message to stdout.
+    The default level is 'info'.
 **/
 function log(message, level) {
-    console.log('[' + (level || 'info') + '] ' + message);
+    if (level === 'error') {
+        console.error('[error] ' + message);
+    } else {
+        console.log('[' + (level || 'info') + '] ' + message);
+    }
 }
 exports.log = log;