Minimal changes to make work with CZMQ

* Fixed use of deprecated/removed sendf/sendfm calls
* Removed fmq_file and fmq_chunk classes -> CZMQ zfile & zchunk
* Build dependency check for CZMQ/2.0.x

Note this is not the final update; I want to modify the FILEMQ protocol
to use the new security mechanisms, and drop its own SASL-style security
negotiation.