Old Canon EOS don't support Shutter commands

Issue #254 resolved
George Hilios created an issue

(Tested with a Canon EOS Rebel Xti 300D)

The following command fails

EDSDK.EdsSendCommand(_cam, EDSDK.CameraCommand_PressShutterButton, (int)EDSDK.EdsShutterButton.CameraCommand_ShutterButton_Completely_NonAF)

To fix this, you can fallback to the TakePicture command to handle older Canons