Proper resource freeing
* all destruction work is done by notify callback
* channel is unreffed right away, so only ref is in watch source
* release everything by deleting watch sources
/CMD command
Executes specified shell command and sends it's output to current buddy.
Shell may be specified explicitly with option cmd_shell or be autodetected from environment.
Usually stderr is discarded, but you can enable its redirection using option cmd_redirect_stderr.