Add support for git-flow 0.4 (bash only).

1. bee8218 Fix for the feature checkout branch argument completion. by Vincent Driessen · 13 years ago
2. 5eda741 add some docs by Zifei Tong · 13 years ago
3. b2667cc fix some bugs by Zifei Tong · 13 years ago
4. 9414b22 finished by Zifei Tong · 13 years ago
5. 85b504a the basic framework is finished by Zifei Tong · 13 years ago
6. 4b64ecc completion of flow subcommand, and its subsubcommands works now by Zifei Tong · 13 years ago