Merge branch 'FreshXOpenSource-master' into gh-master

lib/command.js

@@ -285,7 +285,13 @@ module.exports = function (proto) {
         stdout = stderr = onOut = onErr = onExit = null;
       });
 
-      proc.on('error', cb);
+      proc.on('error', function(err){
+        if (err.code === 'ENOENT') {
+          cb(new Error('Could not execute GraphicsMagick/ImageMagick: '+cmd+" this most likely means the gm/convert binaries can't be found"));
+        } else {
+          cb(err);
+        }
+      });
     } else {
       cb(null, proc.stdout, proc.stderr, cmd);
     }