Estop on subsystem error.

Change-Id: I95e3158caf7766d2fa1668161ad32c3e1ad3ca1e
diff --git a/frc971/zeroing/zeroing.h b/frc971/zeroing/zeroing.h
index 4b21bc4..7b77fdd 100644
--- a/frc971/zeroing/zeroing.h
+++ b/frc971/zeroing/zeroing.h
@@ -226,6 +226,8 @@
   // Returns information about our current state.
   State GetEstimatorState() const;
 
+  void TriggerError() { error_ = true; }
+
  private:
   // Returns the current real position using the relative encoder offset.
   double CalculateCurrentPosition(const IndexPosition &info);