client: clear I_COMPLETE on traceless reply for dentry request

If a request is against a dentry, and we get a traceless reply, clear
the directory I_COMPLETE flag on the parent directory because we can no
longer trust that our cache is complete.

It is possible we could do something a bit more intelligent here, but it
is not trivial because of racing requests, and traceless replies are
rare, so it's not worth the effort.

Signed-off-by: Sage Weil <sage@inktank.com>
doc make_request
fix make_request getattr path