Update Plupload to version 1.5.4

This commit updates Plupload to the latest version (1.5.4).

The JavaScript, Silverlight, and SWF files had changes.

The stylesheets did not have any changes.

**Plupload release notes:**
* 1.5.4: http://www.plupload.com/punbb/viewtopic.php?id=1685
* 1.5.3: http://www.plupload.com/punbb/viewtopic.php?id=1672