go.mod is inside wcfs/ and if `go test ./...` is ran outside of it, it
autodetects to use GOPATH mode and fails to find imports used by wcfs.

To run wendelin.core tests under Nexedi testing infrastructure.

* kirr/t:
  X wcfs: make it to use go modules for dependencies

Still want to preserve GOPATH compatibility as working on several
repositories simultaneously is, unfortunately, currently not good via
modules

https://github.com/golang/go/issues/27542
https://github.com/golang/go/issues/37755

For GOPATH way of work (local development) wendelin.core has to be
symlinked from inside $GOPATH/lab.nexedi.com/nexedi/ and worked through
_that_ directory - else imports inside wcfs will fail.

* master:
  3rdparty/ccan: Update for build fix wrt recent gcc/binutils

We need the following patch of mine:

   http://git.ozlabs.org/?p=ccan;a=commitdiff;h=b97c7f0841f5173a07a2571f2c99f944d8405a90

Else in case of two files used simultaneously the index is messed up.
Fixes test_wcfs_watch_2files and now all wcfs tests pass again.

Reason: see comments.
Prerequisite to fix test_wcfs_watch_2files