And always pass URIs to all file procedures, the ones what didn't
register as "handles remove" will only ever get local file:// URIs.
Change all file plug-ins (also legacy ones) to expect URIs instead
of filenames, and convert to local paths in the plug-in.
The wire protocol should now be almost 100% clean of non-UTF-8 strings.
Implementing a shiny new GimpFileProcedure doesn't mean the libraries
we use to load/save files are automatically capable of handling remote
files, so we still need this flag.
which are GimpProcedure subclasses with API to register as load/save
handlers and their own kind of run functions that get their standard
arguments passed directly instead of packed into a GimpValueArray.
They also register their standard arguments themselves, which removes
quite some boilerplate from load/save plug-ins.
Remove gimpprocedure-private.[ch] because install() and uninstall()
are now virtual functions of GimpProcedure.
