build_id fixes (thanks @mattbasta)

lib/commonplace.js

@@ -286,6 +286,7 @@ function clean(src_dir, callback) {
     var targets = [
         '_tmp',
         'templates.js',
+        'media/build_id.txt',
         'media/imgurls.txt',
         'media/css/include.css',
         'media/js/include.js',
@@ -528,12 +529,11 @@ function build_includes(src_dir, callback) {
         fs.writeFile(build_id_file, new Date().getTime(), function(err) {
             if (err) {
                 console.error('Error writing `build_id.py` to disk.');
-                return;
-            }
+            } else {
                 console.log('Created ' + build_id_file);
-        });
-
+            }
             callback();
+        });
     }
 
     var build = require('./build.js');