Use write_all to write whole buffer

A better way to write a byte string is to use write all so that
`ErrorKind::Interupted` is not returned.

Use `write_all` to write the non-sense (error indication) string to the
writer when we hit the SIGHASH_SINGLE bug.

Author: tcharding

src/blockdata/transaction.rs

@@ -353,7 +353,7 @@ impl Transaction {
             // will result in the data written to the writer being hashed, however the correct
             // handling of the SIGHASH_SINGLE bug is to return the 'one array' - either implement
             // this behaviour manually or use `signature_hash()`.
-            let _ = writer.write(b"[not a transaction] SIGHASH_SINGLE bug")?;
+            writer.write_all(b"[not a transaction] SIGHASH_SINGLE bug")?;
             return Ok(())
         }