RemoteBlobProcessor should print a stack trace of the exceptions it swallows

In order to cope with the dryness of the BlobStore and DataStore API, RemoteBlobProcessor#shouldFetchBinary relies on exceptions to implement part of its logic. While this is a bad development practice, it was the only way to cope with in-memory binary IDs without spending excessive amounts of network and CPU. To Improve the transparency of the system, RemoteBlobProcessor should print a message at WARN level every time it swallows an exception.