A new unit test has been added in consequence.

In environments where there are rules for the email addresses, the "from
address" that owncloud uses has to be configurable.

This patch adds a new configuration variable 'mail_from_address'.
If it is configured, owncloud will use this as the sender of *all*
emails. (OwnCloud uses 'sharing-noreply' and 'password-noreply' by
default). By using the 'mail_from_address' configuration, only this
email address will be used.

When calling fopen() on some storage types, these return false instead
of throwing an exception.

This fix makes sure that in case the stream wasn't opened (for example
when a file doesn't exist any more) the stream isn't wrapped.

Also added 'rb' as another case that doesn't need to be wrapped.

Fixes #6832

There was a syntax error when running tests in PHP 5.3.10.

updated the unit test for OCP\Share::unshareAll() to verify that shares by all users are removed for an item.

The encrypted size was used when calculating folder sizes.
This fix now also sums up the unencrypted size and shows that one when
available.

Storage mount points are not deletable, so make sure that the unlink
operation and its hooks aren't run in such cases.

Note that some storages might recursively delete their contents when
calling unlink on their root. This fix prevents that as well.

Fixes #6526

On SQLite the app order can be arbitrary and cause strange bugs.
On MySQL, the app order seems to be always alphabetical.

This fix enforces alphabetical order to make sure that all environments
behave the same and to reduce bugs related to app loading order.

Fixes #6442

- added isUserAgent() method to OC_Request which makes it possible to
  test it
- OC_Response::setContentDisposition now uses OC_Request::isUserAgent()