Cache interpolated prereceive hook

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Implement auth check

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Allow receiver/authchecker to include arguments

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>
Use PORT environment variable if set

Signed-off-by: Jonathan Rudenberg <jonathan@titanous.com>