Factorization and consistency
- create a fpm_use_error_log() to check when file or stderr should be used
- use it everywhere for consistency
- add some comments
Merge branch 'PHP-5.6'

* PHP-5.6:
  Factorization and consistency - create a fpm_use_error_log() to check when file or stderr should be used - use it everywhere for consistency - add some comments
Fixed typo
Change pm.start_servers default warning to notice

Unlike other settings, this has a perfectly reasonable default, calculated using
a dynamic formula. If the default was hardcoded to "2" or something, then it
would make sense to have a warning, since that could potentially be bad, but for
a dynamically calculated value based on other mandatory settings, a notice ought
to be enough.
move zlog_set_level() again

from fpm_unix_init_main() to fpm_conf_post_process() this time (see #894),
because otherwise nothing in fpm_conf_init_main() obeys log levels
tests for #895
fix test description
Fixed #68458 Change pm.start_servers default warning to notice

Add another test
014 checks that no "notice" are traced when log_level=warning
015 checks that "notice" are traced when log_level=notice