Unsafe (implicit) caching by services flux.mceq_barr and flux.mceq_barr_red

[thehrh]

These do not implement apply_function and thus assume that no preceding service has the ability to reset or vary the "nominal" fluxes. mceq_barr_red states at least that it is intended to be placed after flux.honda_ip.

They should probably have an apply_function, and the user should be able to configure the pipeline such that the current caching behaviour is reproduced (see also #692).