Run sandboxed experiments in a separate process.

You can maintain synchronous execution of experiments using the new '-y' flag.
This commit doesn't add OS limits on the new process; that's coming later.
Add some child process limits.
Remove redundant include.
add help for --synchronous
Move child_info_t to top of file
Merge branch 'fork' of github.com:projectbismark/censorscope into fork