Added missing import in managers.py.
Added missing import in managers.py.

jayzeng/pyes,HackLinux/pyes,aparo/pyes,HackLinux/pyes,jayzeng/pyes,aparo/pyes,haiwen/pyes,Fiedzia/pyes,HackLinux/pyes,mavarick/pyes,Fiedzia/pyes,haiwen/pyes,jayzeng/pyes,mavarick/pyes,Fiedzia/pyes,mavarick/pyes,haiwen/pyes,aparo/pyes