Strings for existing codes in the most used server (OpenSSH) just
repeat the error code name. OTOH we like to have wording of the
strings under our control as much as possible, so we can easier find
and process them. Error strings are still usefull as fallback for
compatibility with future versions of the server.
there was a race between the sendproc putting the request on
the sreqrd[] id and the recvproc handling the response, and
potentially freeing the request before the sendproc() was
finished with the request (or the fid).
so we defer allocating a request id and putting it on the
sreqrd[] stage after we have completely generated the
request in vpack(). this prevents the handling of the request
before it is even sent.
this also means that the SReq should not be touched after
calling sendpkt(), submitreq(), submitsreq().
secondly, putsfid() needs to acquire the RWLock to make sure
sendproc() is finished with the request. the scenario is that
recvproc() can call respond() on the request before sendproc()
has unlocked the SFid.
just use cleanname() to implement pathcat(), which
handles double slashes and ".." elements already.
have to free the partial dir structue on error in
parsedir().
use estrdup9p() instead of strdup().
