[pr2eus] Allow initial av in angle-vector-sequence

[pazeshun]

To fix jsk-ros-pkg/jsk_robot#738

[pazeshun]

Tested in Baxter with jsk-ros-pkg/jsk_robot#741

[pazeshun]

When you do

24.irteusgl$ send *ri* :angle-vector-sequence (list av1 av2) (list 0 :fast) nil 0 :scale 10.0 :allow-initial-av t

you can get following output

$ rostopic echo /robot/limb/left/follow_joint_trajectory/goal 
header: 
  seq: 1
  stamp: 
    secs: 1480988810
    nsecs: 859410541
  frame_id: ''
goal_id: 
  stamp: 
    secs: 0
    nsecs:         0
  id: 1480988810859972236_/default_robot_interface_1480988279165454790_88580_/robot/limb/left/follow_joint_trajectory_11
goal: 
  trajectory: 
    header: 
      seq: 0
      stamp: 
        secs: 1480988810
        nsecs: 859410541
      frame_id: ''
    joint_names: ['left_s0', 'left_s1', 'left_e0', 'left_e1', 'left_w0', 'left_w1', 'left_w2']
    points: 
      - 
        positions: [0.8732185635037704, -0.35051461003181683, -2.58207316120812, 1.451912815733543, 1.266301140399408, 0.9261409006858177, -0.07171360183364295]
        velocities: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
        accelerations: []
        effort: []
        time_from_start: 
          secs: 0
          nsecs:         0
      - 
        positions: [0.6889973932315314, -0.40928755815992957, -2.4558860484054907, 1.2745174531519226, 1.3166378530097589, 0.8595486641241652, -0.007423700762887047]
        velocities: [0.0, 0.0, 0.0, 0.0, 0.0, 0.0, 0.0]
        accelerations: []
        effort: []
        time_from_start: 
          secs: 1
          nsecs: 228141136
  path_tolerance: []
  goal_tolerance: []
  goal_time_tolerance: 
    secs: 0
    nsecs:         0
---

You can set time_from_start to zero only in first point of trajectory (I called that trajectory initial av).

Please review this.

[pazeshun]

I talked to @k-okada in offline.
I understand I should fix baxter_interface.
So is this PR unnecessary? If this PR is totally useless to other robots, I'll close this

[pazeshun]

jsk-ros-pkg/jsk_robot#738 will be fixed in RethinkRobotics/baxter_interface#77