Acceleration limit for backward driving

[Thazz]

When applying acceleration/deceleration limits in velocity iterator, one should be looking for difference in velocity magnitude (absolute value).

robot_navigation/dwb_plugins/include/dwb_plugins/one_d_velocity_iterator.h

Lines 56 to 69 in a17dd62

	inline double projectVelocity(double v0, double accel, double decel, double dt, double target)
	{
	double v1;
	if (v0 < target)
	{
	v1 = v0 + accel * dt;
	return std::min(target, v1);
	}
	else
	{
	v1 = v0 + decel * dt;
	return std::max(target, v1);
	}
	}

Currently, If the robot is driving backwards and its velocity changes from e.g v0 = -1 m/s to target = -1.5 m/s, deceleration limit is used (as v0 > target), although robot is actually accelerating. The same goes for deceleration.

I can provide PR if needed.

[DLu]

Makes sense! Please make a PR.