SFTP: add more unit tests
SFTP: add more unit tests

splitice/phpseclib,thaigialai1987/phpseclib,danog/phpseclib,thaigialai1987/phpseclib,creatuity/phpseclib,danog/phpseclib,phpseclib/phpseclib,melya/phpseclib,kenichiii/phpseclib,kenichiii/phpseclib,splitice/phpseclib,metaclassing/phpseclib,creatuity/phpseclib,paragonie-scott/phpseclib,terrafrost/phpseclib,melya/phpseclib,metaclassing/phpseclib,paragonie-scott/phpseclib