Move func definitions so I know they've been ported

There are comments denoting different parts of the file as to whether
I've put effort into porting the functions over to work with akaros or
not.  Anything below the comment that says "not ported yet" we can't
really rely on being correct yet.
Add ability to get errno and errstr from parlib
Add parlib calls for chmod() and fchmod()

Normally I make direct syscalls rather than going through libc, but the
implementations for chmod and fchmod are now based on the new wstat
syscall, and are a bit more complicated than the other syscalls we've
implemented so far. It's just easier to make the direct libc calls and
not deal with all the convD2M stuff in go at all.
Add syscalls for chmod, fchmod, rename, and fchdir

fchdir and rename are currently still stubbed out (they aren't even
implemented in akaros glibc yet!), but functionality for chmod and
fchmod is now in place based on the new parlib calls for
chmod()/fchmod() and errno()/errstr().