Create sftp.php

Adapter for SFTP using the pure php SSH library phpseclib
Update apps/files_external/appinfo/app.php

Adding support for SFTP
Update apps/files_external/lib/config.php

Adding support for SFTP mounts
Update apps/files_external/lib/sftp.php

Added checks for host keys and added exceptions thrown if constructor fails.
Update apps/files_external/lib/sftp.php

Added a little better exception handling, hopefully making it a little more robust
Update apps/files_external/lib/sftp.php

Added copyright notice
Added phpseclib to files_external as 3rdparty
Update apps/files_external/lib/sftp.php

Updated to using local 3rdparty + added a few missed braces.
Update apps/files_external/lib/sftp.php

Created test() function as per @pull/1031
Update lib/filestorage/common.php

Added function to clean a path
Update apps/files_external/lib/sftp.php

Added cleaning the root path
Merge remote-tracking branch 'upstream/master'

Conflicts:
	apps/files_external/lib/config.php
Update lib/filestorage/common.php

Small cleanup
Merge branch 'master' of https://github.com/owncloud/core

Conflicts:
	apps/files_external/appinfo/app.php
Deleted phpseclib/tests
Modified to new class structure
Merge branch 'master' of https://github.com/hkjolhede/owncloud_core
corrected namespace
Update to conform to API changes
Added unittest