Fix potential deadlocks in AbstractRequestHandler#start_main_loop.
Fix potential deadlocks in AbstractRequestHandler#start_main_loop.

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