Delint test_sftp (remove unused imports and unused variables, remove excess whitespace, move imports to top, remove semicolon terminator)

--HG--
extra : source : 01df712a396de5fa7e1c0cc265411fdb2bbc5f41
Adding test capturing desired behavior and demonstrating issue #142.
Remove 'file_size' check from tests. The docstring indicates this parameter is to be passed to the callback, and there's no reason to think this parameter is relevant in affecting whether a useful stat object has been passed (especially when the 'confirm' parameter is explicitly supplied for that decision. This fixes #142.
Update NEWS per #142
Remove pointless & outdated version/release crap from README
Merge branch '1.9' into 1.10
Merge branch '1.10'
Merge branch '1.10' into 143-int
Dumb format tweak to NEWS
Merge branch '1.10'

Conflicts:
	NEWS
Fix bug that leaves fds in select after EOF received
Changelog re #154
Bump version to 1.10.1
Merge branch '1.10'

Conflicts:
	NEWS
Update demo.py

why import threading?
Store hostname hashes in memory rathen than the non-hashed host entries. Also assures that the host entries in known_hosts get saved in hashed format as it is currently standard in OpenSSH.
Assure that host entries in known_hosts files do not duplicate endlessly if keys from known_hosts are loaded via HostKeys.load() more than once (e.g. for refreshing the list of known hosts during runtime).
Load host entries from the known_hosts file(s) before writing the file from RAM to disk. Avoids loss of host entries in case other SSH clients have written to the known_hosts file(s) meanwhile.
do not write ,,garbage'' to known_hosts file(s)
Changelog re #87