This Library is no longer in use, we haven't sold the original style Motorshields for many many years. Apparently they are now natively supported in http://www.airspayce.com/mikem/arduino/AccelStepper/ So please go there :)
Metori/AccelStepper
A small fork of AccelStepper v1.3 with AF_motor (Adafruit motor shield) support!
C++NOASSERTION