update to latest, use local cvsync feed

previous builds used either external cvs->git mirrors:
http://anoncvs.estpak.ee/cgi-bin/cgit/openbsd-src/
https://bitbucket.org/braindamaged/openbsd-src

Both of these have proven somewhat unreliable (missing commits, days
without updates), so I switched to a local cvsync script to do the
imports.
add source synchronization scripts
sync tweaks (absolute path requirements for cvsync are annoying)
integrate getentropy_linux and arc4random

this replaces libottery on Linux platforms