Update SessionExist to close the db connection

close the mysql connection

use connection pool for redis, support auto connection

fix #453

support redis cache auto connection

* this will support auto-connection

1. mysql fix last access time not update
2. mysql & redid Release when data is empty
3. add maxlifetime distinct Gclifetime

change a log

Error page improvements

// the follow code is write in modules:
// GR:=NewGroupRouters()
// GR.AddRouter("/login",&UserController,"get:Login")
// GR.AddRouter("/logout",&UserController,"get:Logout")
// GR.AddRouter("/register",&UserController,"get:Reg")
// the follow code is write in app:
// import "github.com/beego/modules/auth"
// AddRouterGroup("/admin", auth.GR)

add comments in logs package.