fix session garbage collector
fix session garbage collector

on debian systems gc_prbability is 0 by default because session garbage
is collected using a cron job

also set gc_divisor to a useful default value, some servers would use 100 instead
which is probably too much

darimpulso/koala-framework,Ben-Ho/koala-framework,yacon/koala-framework,Sogl/koala-framework,nsams/koala-framework,Sogl/koala-framework,koala-framework/koala-framework,darimpulso/koala-framework,nsams/koala-framework,yacon/koala-framework,kaufmo/koala-framework,yacon/koala-framework,kaufmo/koala-framework,Ben-Ho/koala-framework,nsams/koala-framework,koala-framework/koala-framework,kaufmo/koala-framework