Support KDC being a master and slave at the same time

[macrotex]

Support a server running both ipropd_master and ipropd_slave.

Cascading KDCs is one use case where this would be helpful: KDC A replicates from KDC B which in turn replicates from KDC C. In this scenario, KDC B needs to be both a master and slave. This sort of cascading makes it possible to have more efficient architectures when large numbers of slaves are needed.