Explicitly dist the examples again.

Some versions of autotools seem to do this automatically because
these are dependencies of the gresources .c files.
Use G_STRFUNC on all std::cerr messages.

I really need to invent some more concise way to do simple
error checks and logging.
GResource building: Fixes for builddir!=srcdir.
GResource building: Use the --internal option.
1.25.3