[ofiwg] detecting FABRIC_DIRECT mismatch

[Hefty, Sean]

> That is still an ABI change, you can't have
> 
>  fi_foobar(struct fi_foo *)
> and
>  fi_foobar(struct fi_foo_verbs *)
> 
> With the same symbol name - that is an incorrect way to use dynamic
> library symbols.

To be clear, what actually gets replaced is the app invoking

	object->function_set->foobar(struct fi_foo *)

versus

	fi_foobar(struct fi_foo_prov *)

fi_foobar is not exported from a non-direct build.