Failed Installation Recovery

Initially I launched the installer from Windows Explorer, and the installation failed because the git command wasn't in my path. I then tried to launch the installer from msysgit and this failed because the git-credential-winstore.exe already existed in %AppData%\Roaming\GitCredStore. 

I modified the Program.cs to see if the .exe exists before copying and if it does delete the current .exe and then copy again.