cmogstored 1.7.1 - Linux 5.0/5.1 epoll_pwait workaround

The Linux kernel bugfix should hit mainline and stable kernels,
soon.  But there's no reason for us to be caring if errno is
EINTR or not...

cf. https://lore.kernel.org/lkml/20190427093319.sgicqik2oqkez3wk@dcvr/
    https://lore.kernel.org/lkml/20190507043954.9020-1-deepa.kernel@gmail.com/

There are also some minor build/test updates since v1.7.0 (2018-12-18):

      test/mgmt-usage.rb: fix mismatched indentation warning
      add .gitattributes for Ruby files
      test/mgmt_auto_adjust.rb: improve diagnostic messages
      .gitignore: add extra ignores for gnulib in Debian 9
      notify.c: workaround epoll_pwait bug in current Linux 5.0/5.1
      doc: remove mailing list subscription info