Add failing test reproducing issue #1015.

There is a race condition when connect and bind on a new inproc
endpoint happen "simultaneously" in threads.  Causes the error:
  Assertion failed: ok (ctx.cpp:474)
Mark failing test for issue #1015 as XFAIL
Revert "Mark failing test for issue #1015 as XFAIL"

This reverts commit b6c577a9ecaa3d20b82baf704a90e5555f850be9.
Merge pull request #1020 from jemc/inproc_simult

Add failing test reproducing issue #1015.