Pathpreview

1)
Enable path preview arrows, click on a destination and vary the reserve TU buttons.   Currently the path preview is not updated.  Fix updates the colors:
![screen041](https://cloud.githubusercontent.com/assets/1824834/2647273/c22c746e-bf48-11e3-8728-558e3cb06703.png)
![screen042](https://cloud.githubusercontent.com/assets/1824834/2647274/c3bd2bca-bf48-11e3-9ef6-1fffbae8ec70.png)
![screen043](https://cloud.githubusercontent.com/assets/1824834/2647275/c5409590-bf48-11e3-99ba-5442c32b7e7b.png)
![screen044](https://cloud.githubusercontent.com/assets/1824834/2647276/c6bc3d0c-bf48-11e3-857f-0ae8d091b8c7.png)
![screen045](https://cloud.githubusercontent.com/assets/1824834/2647277/c8219ad4-bf48-11e3-8151-fed0b498975a.png)

2) 
Enable path preview arrows, click the "Don't reserve TUs" button, expend enough TUs so that unit cannot make an aimed shot, click "Reserve TUs for Aimed Shot" button, click on a destination tile.  Currently the arrows are green. Fix ensures arrows are yellow

Su-bin needs 42 time units for an aimed shot.  Before update:
![screen047](https://cloud.githubusercontent.com/assets/1824834/2647378/fd836e22-bf49-11e3-9718-813ec337803e.png)
After update:
![screen048](https://cloud.githubusercontent.com/assets/1824834/2647381/00a76838-bf4a-11e3-8bc6-03ded173b23d.png)