ScriptFu: cleanup messages to the terminal

Lloyd Konnekerrequested to merge
bootchk/gimp:SFcleanDebug into master

Cleanup.

No changes to functional code, only to messages.

Reduced the volume of DEBUG messages in ScriptFu.

Reduced a WARNING to an INFO when fewer or more args are given for a PDB call. Discussed in #12499 (closed)

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