Include date modified in upload url to download a fresh copy of the attachement if the original document has changed

When a new attachement in an existing note is uploaded it overrides the existing one. Problem is, since the old one is cached you can't download the new version since the browser keeps downloading the old cached version of the attachement.

The proposed fix is to include the modified date as the part of the attachement url, so whenever a document gets updated a new "unique" url is generated and new attachement is being downloaded. 

This has been raised in Sugar bugs database: http://www.sugarcrm.com/support/bugs.html#issue_63983