This mode/setting is unusable left-over from SHA-256 cgminer. It does not work with Scrypt or other algorithms that are used in sgminer. Removed in single commit so it can be used as reference, if benchmark mode is added in the future.
Doc in `doc/configuration.md` (has to be started sometime, no?).
Configuration function has to be lamely-named set_algo(), because
set_algorithm() is already declared in algorithm.h (prevent namespace
conflict).
algorithm has to be added as global variable due to the way the
callback is done (by CCAN/opt, which in itself is nice).
This can be cleaned up significantly by (at least) introducing a
global configuration struct, but there is no reason to do it now
just for this - better a wholesale manana.
