By default the new API will be used. But if we build with
GIMP_DEPRECATED_REPLACE_NEW_API macro, then the same function names will
call the old API with ids.
This way, we don't have to update all our plug-ins at once (which I
tried and is very tedious work).
Note that bindings won't have access to the deprecated API at all.
We were only able to translate selections and layers (bot not channels
and paths) via the PDB, this new procedure fixes that. Deprecation of
old API and some more transform consistency to follow...
Works for all item types, and has much less functions and parameters
than the drawable transform API because it uses the new context
states. Untested and not finished!