* Fixed an SCP path traversal issue. Thanks go to Jaden Furtado for
reporting this issue.
* Expanded previous fix to block unsafe user substitutions in server
config. Thanks go to GitHub user cesabici-bit for reporting this
issue.
* Fixed default value for reuse_address and reuse_port, matching
the behaavior of asyncio.create_server(). Thanks go to Alexander
Shlemin for reporting the inconsistency.