28f1cb9da2
This new field will be used to describe certain properties of some muxes. For now we only add MX_FL_CLEAN_ABRT to indicate that a mux is able to unambiguously report aborts using CS_FL_ERROR contrary to others who may only report it via a read0. This will be used to improve handling of the abortonclose option with H2. Other flags may come later to report multiplexing capabilities or not, support of client/server sides etc.