- include return value of the IPC_CHILD payload in the END fifo message - big rework where now i use a lockfile to keep pending children from   starting: 	- IPC_MASTER makes the file and sets it mode 0000 	- IPC_CHILD temporarily sets its umask to 0000 and then loops on 	  trying to write to the file, which will fail until the file 	  is gone. 	- IPC_MASTER removes the file in place of the old "SIGCONT" to 	  a SIGSTOP'ped IPC_CHILD, allowing a new child to drop one and 	  proceed - IPC_END now gets its SIGCONT when IPC_MASTER has *completed* teardown   actions, not simply as an acknowledgement that IPC_MASTER *received*   the teardown request (we'll see if that has any material effect). - it runs reliably now for the "only ever one IPC_CHILD invoked" case,   which was a tricky corner, so check it in
- include return value of the IPC_CHILD payload in the END fifo message
- big rework where now i use a lockfile to keep pending children from
  starting:
	- IPC_MASTER makes the file and sets it mode 0000
	- IPC_CHILD temporarily sets its umask to 0000 and then loops on
	  trying to write to the file, which will fail until the file
	  is gone.
	- IPC_MASTER removes the file in place of the old "SIGCONT" to
	  a SIGSTOP'ped IPC_CHILD, allowing a new child to drop one and
	  proceed
- IPC_END now gets its SIGCONT when IPC_MASTER has *completed* teardown
  actions, not simply as an acknowledgement that IPC_MASTER *received*
  the teardown request (we'll see if that has any material effect).
- it runs reliably now for the "only ever one IPC_CHILD invoked" case,
  which was a tricky corner, so check it in

jrrs/sh