spawn: fix possible NULL dereferences
simplify file_readall()
spawn: do not use syslog calls in the child process

The syslog routines uses private mutex so it can cause
various crashes and other misbehaviour.

Use pipes to send messages from the child processes.
spawn: implement spawn_and_give_stdout()
IPTV: add pipe:// handler to read MPEG-TS stream from an external program