The system supports uploading files with long names, but file names will now be truncated only if they exceed 150 characters.
Anything up to 150 characters will upload without truncation.
PS: View Drag, Drop & Upload Files to Amazon S3, a Salesforce AppExchange app for moving files from Salesforce to Amazon S3: https://appexchange.salesforce.com/appxListingDetail?listingId=a0N3000000B5ZPqEAN