otherwise, implicit transitive linking will pull in the installed
libs, not the ones from the source tree, and the build can fail when
any of the libs' APIs changes.
Also remove some useless #includes.
Otherwise people will install older versions and won't understand why
the plug-ins won't work. It's just a little annoying that these version
strings have to be hardcoded this way. We could add macros in a header,
but that would be only half a solution. Ideally we'd rather have some
discovery logics at some point.
...with known plugins
Add new plug-in file-raw-placeholder.c that registers itself for
loading all RAW formats from file-raw/file-formats.h, but does nothing
except returning an error message pointing to darktable and
RawTherapee.
When no real RAW loader is installed, this plug-in is selected
automatically as RAW loader, otherwise the first installed RAW loader
is used. Selecting another in prefs still works as before.
