Updated Downloader to set the file's last modified time using the "La…

…st-Modified" HTTP header. This fixes an issue where the "If-Modified-Since" HTTP header was ignored when issuing multiple requests in a short period of time. Using an exact date fixed the issue though the cause is unclear. (Perhaps some intermediary caching layer interpreted the header differently?). Closes #8

scripts/downloader.js

@@ -75,7 +75,13 @@ var downloadImage = function (inputUri, downloadDir, callback) {
     // Else save
     res.pipe(fs.createWriteStream(filePath))
        .on('close', function () {
-         return callback(undefined, { 'path': filePath, 'statusCode': res.statusCode, 'statusMessage': res.statusMessage })
+          var lastAccessed = lastModified = new Date();
+          var lastModified = res.headers['last-modified'] ? new Date(res.headers['last-modified']) : lastAccessed;
+
+          // update the last modified time of the file to match the response header
+          fs.utimes(filePath, lastAccessed, lastModified, function (err) {
+            return callback(err, { 'path': filePath, 'statusCode': res.statusCode, 'statusMessage': res.statusMessage })
+          });
        });
   }).on('error', function(err) {
     return callback(err);