Let's check the second time a global counter of "ha_warning" messages, if
zero-warning is set. And let's do this just before forking. At this moment we
are sure, that we've already done all init operations, where we could emit
"ha_warning", and we still have stderr fd opened.
Even with the second check, we could lost some late and rare warnings
about failing to drop supplementary groups and about re-enabling core dumps.
Notes about this are added into 'zero-warning' keyword description.
fcd4bf54c8
