Use inferno read/write instead of pread/pwrite

Passing in a -1 offset was just causing rread to abort.  For now, we'll
want the file offset tracked in the chan, like with normal FDs.
All qlocks are initialized

Or at least those I could find.  We'll probably need to make other
newconv() methods for all the protocols to do other initialization.

I also initted similar sync variables when I saw them.