This patch set is now the combination of the one patch against RPCS and the two patches
against RPCC, I sent out on friday. The reason to combine these three patches in one patch
set is, that both provider - RPCS and RPCC - look very similar now. This brought me to the
idea, that it is possible to also define a common interface for instances providers - as
this is already done for associations -, where the common functions could do a main part
of the error handling (which is currently done again and again in each single provider
itself).
In addition patch 4 updates HS (thanks to Kaitlin) with the new interface of RPCS.