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
Added creation of dir for shared file env encryption keys
Added comment to use multiKeyEncrypt
Merge branch 'master' into files_encryption
Added two hooks: pre_unshare and pre_unshareAll, useful for files_encryption
Merge branch 'master' into files_encryption
Adding sharing support: added new method in Keymanager setShareKey()
Added notes in proxy{} and stream{} pointing to share support
Fix sharing issue with collection and children mismatches
Merge branch 'master' of github.com:owncloud/core
Merge branch 'files_encryption'
Work on util: findFiles() and encryptAll(); both close to working
Ecnryption unit tests are failing, recursion in filecache{}
Fixed many coding guidelines issues
Continued work on upgrade path via login hook listener
New spec file with notes
Update lib/filestorage/common.php

Added function to clean a path