fix bug, redis session doesnt work
bug fix, session stored in redis cannot be deleted
bugfix, delete the sid if it's values is empty

* regenerate sid, if the old key doesn't exists, set the new one directly
fixed bug: in logs package check if platform is windows
Merge pull request #487 from cloudaice/log-feature

fixed bug: in logs package check if platform is windows
Merge pull request #474 from pengfei-xue/develop

fix bug, redis session doesnt work
Add a Debug method to allow for debugging individual queries:

o := NewOrm()
u := &User{Name: "Kyle"}
o.Read(user, "Name") // logs nothing

u2 := &User{Email: "kylemcc@gmail.com"}
o.Debug().Read(u2, "Email") // logs debug query

qs := o.Debug().QueryTable("users")
qs.Filter("Profile__Id", 10).One(u) // logs debug query