check if the decrypted private key is valid on login and on read/write files
allow the user to login but do not allow upload and show error message on the web

Conflicts:

	apps/files_encryption/appinfo/app.php
code optimized and cleaned up unused vars
introduce decryptPrivateKey() method which also checks if the result is a valid private key to avoid additional checks on various places

Conflicts:

	apps/files_encryption/lib/session.php
control files are no longer needed, remove them from the tests
$session->setPrivateKey expects only one parameter
let user update private key password in case it was changed from outside, e.g. external auth back-ends
added test for decryptPrivateKey()
use generated private key fro m setUp()
reformat code

Conflicts:

	apps/files_encryption/lib/session.php
	apps/files_encryption/lib/util.php
fix password change when files_encryption app is disabled

Conflicts:

	settings/ajax/changepassword.php
fixed typo
changed redirect handling
better handling for http post
link directly to the encryption settings
improved label for the password recovery feature
improved error msg and removed duplicate string
only show personal settings if the recovery feature is enabled or if no private key is set
tell the user what he can do to regain access to his files
allow to press enter to update the password