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.

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