Run gofmt on client_integration_test.go
Add integration test flag for sftp binary path
Merge pull request #22 from fd0/flags-for-tests

Flags for tests
Correct typo
Add sftp.NewClientPipe()

This method returns a Client from a pair of pipes.  This can be used for
connecting to an SFTP server over TCP/TLS or by using the system's ssh
client program (e.g. via exec.Command).

An Example function is added, and the client integration test uses the
function.