Update generic troubleshooting tips: recommend looking in the Rails log files as well

[ci:skip]
Remove some unused comments
...
Sort apache2/ConfigurationFields alphabetically after sorting on size
Embed descriptions in ext/apache2/ConfigurationFields.hpp
Introduced the `PassengerErrorOverride` option

This allows HTTP error responses generated by applications to be intercepted
by Apache and customized using the `ErrorDocument` directive.