Allow (script-fu-use-v3) in script, or in SF Console.
Definitive description is in script-fu/docs/using-v3-binding.md
Makes SF interpret v3 of SF dialect.
- marshals single return value from PDB without wrapping in list
- marshals boolean return value from PDB as #t #f instead of integers
- marshals boolean to PDB from #t and #f or TRUE and FALSE
- marshals void return from PDB as () instead of (#t), but that is moot.
The version of SF dialect is distinct from the version of the PDB API.
Dialect v3 is opt-in: the initial dialect of all SF tools remains v2.
Commit also allows #t,#f for defaults of SF-TOGGLE instead of TRUE, FALSE
but that is an independent enhancement (but closely related.)
Affects interpreter state of the current process.
Not an attribute per se of a plugin.
While in this state, a plugin should not call PDB procedures
which are themselves v2 script plugins,
or a few utility scripts in script-fu-util.scm,
but that is rarely needed.
Does not remove symbols TRUE and FALSE from dialect.
A script can also call (script-fu-use-v2) to revert.
That is also discouraged but useful e.g. for testing.
