Add warning to wayland buffer

...to prevent devs from using it as a `ws_buffer` and filing bug-reports
because the method segfaults.
Fix wayland buffer usage in surface commit code
Merge pull request #634 from neithernut/add-compositor-wayland-buffer-warning

Add warning to wayland buffer
Add zindex member for surface
Merge pull request #623 from matthiasbeyer/add-zindex

Add zindex for ws_surface
Add method to manager for shutdown
Do not try to unlock the processor if locking failed
Rewrite portion of flushing function

...to account for
 * EWOULDBLOCK
 * logging
 * need for closing down the connection through the connection manager
Make ws_object_attr_read() consider basetype
Make ws_object_attr_write() consider basetype
Add object type for testing basetype considering algorithm
Add test for getting attribute type with basetype consideration
Add test for attribbute reading with basetype checking
Add attribute writing test with basetype checking
Merge pull request #642 from neithernut/add-connection-shutdown

Add connection shutdown through connection manager
Rewrite error handling and deinitialization in dispatcher

...acounting for:
 * EWOULDBLOCK
 * error reporting
 * new connection shutdown method
Merge pull request #631 from matthiasbeyer/add-obj_attr_getter_setter_basetype

Add attribute reading/writing with basetype checking
Merge pull request #644 from neithernut/add-connector-close_on_eof_or_error

Rewrite error handling and deinitialization in dispatcher
Add x/y position to abstract shell surface