multi-threading fix and enhancements

[dirkpetersen]

As it turns out, Claude actually 'forgot' to take the multi-threading logic from pwalk, ah well, now fixed and added

• --force-group-writable option to implement a parallel chmod -R g+rw
• multiple --exclude possible
• --threads to change the default of 32 threads
• if setuid bit in binary active, replace target folder with current one