Use nftw instead of our own dir scanning code.

Among other things, this handles symlinks better.
Reorder syscall tests in child loop

This way, we retry faster on disabled syscalls.
Fix handling of forced 32bit syscalls.

if we ran trinity -c lstat on a 64bit machine, we would never
do any syscalls, because lstat only exists on 32bit.
Check files are readable before adding them to the file list.

- Avoid -EISDIR on directories
- consolidate stat'ing code to one function.
remove debug code
execve sanitise improvements
path mangling.
clean up the page_rand randomizer some
generate a page of unicode garbage