Bump default passenger version to the latest bugfix release 4.0.42.
Default to Ruby 2.1.2 as packages are now available.
Make PassengerFriendlyErrorPages configurable.

cr https://cr.amazon.com/r/1909780/
in adition to nil check if database is empty

see https://tt.amazon.com/0032177050

cr https://cr.amazon.com/r/2491704/
Set default patchlevel for Ruby 1.9.3 to p547.
changed rails driver auto-detection to support postgresql

cr https://cr.amazon.com/r/2515646/
Don't try to install mysql libraries as they are already available.

cr https://cr.amazon.com/r/2554922/