Clean up some GeglBuffer functions
TileHandlerZoom: Use tile storage members directly
Always propagate the *FLAGS variables to g-ir-scanner (bug 722480)

The issue was not that they got un-escaped too many times but too
few. Expanding them here seems to get the correct behavior.
Fix bliting from a cached node (bug 722963)

When processing a cached node the result was moved to
operation_result but not the context's "output" pad.
Allow the operation_result object to leak out of the
loop so the final output can use it directly instead
of querying the context again.
Updated German translation
TileStorage: Cleanup & remove dead code

* Move mutex to _init instead of _new.
* Remove dead loop (the chain is always empty when _new is called).
Remove duplicate definition of gegl_tile_get_data
TileStorage: Remove duplicate declaration
Add flush-on-destroy property to TileBackend

Use a boolean to control whether or not data gets flushed when a
buffer is destroyed instead of sniffing the object type.