Fix locking in StandardApplicationPool::toString().
Fix locking in StandardApplicationPool::toString().

This bug seems to be what causes more backend processes to be spawned
than is allowed by the 'max' setting.

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