load rally and rally_land points from a file.
         returns number of points loaded

def load(self, filename):
        '''load rally and rally_land points from a file.
         returns number of points loaded'''
        f = open(filename, mode='r')
        self.clear()
        for line in f:
            if line.startswith('#'):
                continue
            line = line.strip()
            if not line:
                continue
            a = line.split()
            if len(a) != 7:
                raise MAVRallyError("invalid rally file line: %s" % line)

            if (a[0].lower() == "rally"):
                self.create_and_append_rally_point(float(a[1]) * 1e7, float(a[2]) * 1e7,
                                                   float(a[3]), float(a[4]), float(a[5]) * 100.0, int(a[6]))
        f.close()
        return len(self.rally_points)