For some symbols defined or deprecated in GIMP 2 and obsolete in GIMP 3.
ScriptFu automatically loaded these definitions
during development of GIMP 3 (from 2.99 to 3.0rc1).
That is no longer the case.
A third-party script CAN load them explicitly.
We discourage that, for scripts to be shared,
but it is convenient for private use.
PDB-compat-v2.scm is also an executable definition of renamings,
useful as a cross check of published documents re porting plugins
from v2 to v3.
So an editor recognizes them.
Renames script-fu.init to init.scm since that is a Scheme convention.
Scheme interpreter maintainers expect that name.
The same name as upstream TinyScheme.
When mingled with plugin scripts, they needed a non-standard suffix .init.
Which makes an editor not recognize them.
Which deviates from Scheme convention for the main init script: init.scm.
The separate directory is also a place for script authors
to put Scheme scripts they don't want loaded automatically,
but when a script calls Scheme load function.
No change to observable behavior in the app or ScriptFu tools.
