New small feature and a few bug fixes related to IPC

[lsnider]

Feature

• add ability for child to send a message to the parent via child_send_result_to_parent
• switched to async signal handling
• post results now includes children identifier in callback

Bugs

• fixed issue where caller could call register_parent_prefork() without an array but the code relies on it being an array

• fixed an issue where a signal interrupting socket_receive or socket_send would cause the protocol to get out of sync. without the signal block, sometimes the payload header was being partially consumed resulting in a mixup of the payload header and payload

• fixed an issue where a signal interrupting fetch_results could remove a pid from $this->forked_children, get added back in with just a last_active field and later throw an undefined index error. there was a fix in place to fix barracuda bug BNBS-23987. the fix helped with the race condition but did not solve it. in addition, the fix destroys child results that might have not been processed yet. the solution was to disable ticks during the fetch_results function and remove the earlier fix attempt.

• fixed an issue where the IPC sockets were not being stored for helper children

• fixed an issue where helper children were not calling srand causing the helper children to get same random numbers as the parent

• fixed an issue where helper children were not honoring the respawn parameter

[devsibwarra]

Tried to fix some codeclimate issues and made it angrier. I'll leave this in the capable hands of @ablyler :)