…ts via 'set :server, handler' if Rack::Handler::Thing doesn't exist. This lets special capitalziation cases like FastCGI, CGI, and WEBrick be handled easily.
…h is code for 'all of them'
… borrowed from rails (compilable.rb)
…development mode. Default is $0. This is for situations where $0 isn't the Sinatra application
…d an :app_file option to define which file to reload