* maint:
  crash when closing an ypipe -- fixed

* maint:
  if TSC jumps backwards (in case of migration to a different CPU core) latency peak may occur -- fixed

Conflicts:
	src/app_thread.cpp

if TSC jumps backwards (in case of migration to a different CPU core) latency peak may occur -- fixed

The flag in the socket has clear semantics now -- it tracks whether corresponding context was closed, it doesn't track whether zmq_close was called on the socket itself

termination of pipe via delimiter message could stuck when no data were read from the pipe (because connection wasn't active) -- fixed

* maint:
  values of RATE, RECOVERY_IVL and SWAP options are checked for negative values