Correctly detect Ruby 1.9's development headers.
Correctly detect Ruby 1.9's development headers.

bf4/passenger,erikogan/passenger,gravitystorm/passenger,clemensg/passenger,jawj/passenger,gravitystorm/passenger,antek-drzewiecki/passenger,openSUSE/passenger,clemensg/passenger,gravitystorm/passenger,openSUSE/passenger,fabiokung/passenger-debian,antek-drzewiecki/passenger,erikogan/passenger,cgvarela/passenger,bf4/passenger,erikogan/passenger,cgvarela/passenger,antek-drzewiecki/passenger,bf4/passenger,cgvarela/passenger,pkmiec/passenger,bf4/passenger,phusion/passenger,fabiokung/passenger-debian,jawj/passenger,fabiokung/passenger-debian,phusion/passenger,openSUSE/passenger,cgvarela/passenger,phusion/passenger,fabiokung/passenger-debian,clemensg/passenger,kewaunited/passenger,fabiokung/passenger-debian,pkmiec/passenger,phusion/passenger,bf4/passenger,erikogan/passenger,clemensg/passenger,antek-drzewiecki/passenger,gravitystorm/passenger,antek-drzewiecki/passenger,phusion/passenger,pkmiec/passenger,fabiokung/passenger-debian,kewaunited/passenger,phusion/passenger,jawj/passenger,clemensg/passenger,pkmiec/passenger,phusion/passenger,antek-drzewiecki/passenger,jawj/passenger,pkmiec/passenger,cgvarela/passenger,openSUSE/passenger,openSUSE/passenger,pkmiec/passenger,gravitystorm/passenger,kewaunited/passenger,cgvarela/passenger,openSUSE/passenger,pkmiec/passenger,clemensg/passenger,erikogan/passenger,erikogan/passenger,kewaunited/passenger,phusion/passenger,jawj/passenger,kewaunited/passenger,cgvarela/passenger,clemensg/passenger,antek-drzewiecki/passenger,jawj/passenger,kewaunited/passenger,kewaunited/passenger,clemensg/passenger,bf4/passenger,kewaunited/passenger,jawj/passenger,antek-drzewiecki/passenger,gravitystorm/passenger,bf4/passenger,cgvarela/passenger