Add an installer for the msysgit environment
Add an installer for the msysgit environment

This installer:
- detects the Git installation path
- checks prereqs (git, getopt.exe)
- delete old gitflow install
- install gitflow files

"Access denied" errors are detected and the user is given advice in that case (
use full administrator rights).

dhilgarth/gitflow,JelteF/gitflow,oddnoc/gitflow,yonglehou/gitflow-1