Update .gitignore to exclude *.exe under Cygwin
Clarify configure messages for --with-poller=...
Merge pull request #894 from olafmandel/Cygwin_gitignore

Update .gitignore to exclude *.exe under Cygwin
Merge pull request #895 from olafmandel/LIBZMQ_CHECK_POLLER

Clarify configure messages for --with-poller=...