Guard against socket.gets being nil

In the situation where the socket has only one line to respond with, any
following gets to the socket need to take care to not assume there is a
non-nil response.
Fixed missing requires in test files

Missing requires in test files made them fail when run one at a time.
test_all.rb would sometimes fail when the test order changed, because of this.
implement a experimental keepalive feature
Merge pull request #114 from GautierMinster/fix-tests-requires

Fixed missing requires in test files
Merge pull request #112 from daisybill/master

Guard against nil socket.gets responses
Merge pull request #116 from noric/feature/keepalive

implement a experimental keepalive feature #115
Automatically forward environment variables defined in OpenSSH config files

Also accept `:send_env` option on `Net::SSH.start`
Merge pull request #118 from fnordfish/allow-sendenv

Automatically forward environment variables defined in OpenSSH config files
fix for 'Could not parse PKey: no start line' error on private keys with passphrases'
remove comment
Merge pull request #120 from metametaclass/master

fix for 'Could not parse PKey: no start line' error on private keys with passphrases
Version bump