Merge pull request #531 from ouziel-slama/develop

hex string in blocks.previous_block_hash
Pylint‐Recommended Cleanup

Files touched: `counterparty-cli.py`, `counterpartyd.py`

- Removed unused imports.
- Whitespace
- Indentation
- Multiple statements on one line
Pylint‐Recommended Cleanup

Files touched: `send2.py`

- Whitespace
- Undefined variables
fix sign_tx