WSGI: Use select.poll instead of select.select .

Avoids the infamous 1024 file descriptor limit. No functional change
expected, as it seems unlikely this bug ever triggered on waitress-managed
file descriptors.
7 jobs for master in 0 seconds (queued for 5 seconds)
Status Job ID Name Coverage
  External
passed ERP5.CodingStyleTest-Master

00:41:30

passed ERP5.PerformanceTest-Master

00:24:14

failed ERP5.UnitTest-Master

01:42:42

failed ERP5.UnitTest-Master.Medusa

01:44:07

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

00:10:02

passed SlapOS.Eggs.UnitTest-Master.Python2

00:08:28