Update BlobRestProxy.php

Allow upload of >4Gb files
http://msdn.microsoft.com/en-us/library/azure/ee691964.aspx : 
Block IDs are strings of equal length within a blob. Block client code usually uses base-64 encoding to normalize strings into equal lengths. When using base-64 encoding, the pre-encoded string must be 64 bytes or less. Block ID values can be duplicated in different blobs. A blob can have up to 100,000 uncommitted blocks, but their total size cannot exceed 400 GB.

http://php.net/manual/fr/function.str-pad.php