change all the frontends to provide the warning callback in the
miscelaneous table instead of using the warn_user function.
Changing all the warn_user callsites still requires completion.
When the operations tables were created the browser table was renamed
to miscellaneous except the actual rename patch was never applied,
this fixes that situation.
This removes the global PDF_Password interface that had completely
bitrotted and moves it into the standard misc operation table with a
sensible defualt implementation.
This also cleans up and fixes the gtk frontend implementation of the
pdf password callback so it compiles.
Finally this moves the implementation to a sensible place alongside
the other exporters reducing target makefile complexity futher.
This is the initial part of a series which splits up the API interface
definitions for the frontends removing a great deal of unnecessary file
inclusion and further isolates the fronted API usage from the core
Vincent Sanders