don't generate stubs for inherited interfaces

Those stubs should be linked from the inherited interfaces' *-client.o
instead.
demote a FIXME in analyse.c

Janitorial stuff to make FIXMEs something that's worth doing in the near term.
pop g_error() when a vtable slot isn't filled

Could instead print a dummy vtable slot, but w/e. This is mostly to satisfy
the clang static analyzer.