Indicate direction of steepness in road building mode

http://wl.widelands.org/forum/topic/1124/

When building roads, I sometimes find it unclear whether I'm building a road up a hill or down a hill.

I propose flipping the orientation of the steepness indicator to indicate whether it is uphill or downhill from the current location.

The code change is trivial - I've done it locally in order to get a screenshot to indicate the possibility, but have opened this topic to discuss if its something that people want or don't want.

This screenshot shows that it is downhill in all directions.

For directions west of the flag the indicator is flipped compared to directions east of the flag, so if you are building a road on the side of a hill, where the west is higher, then all indicators will be of the > style. If the east was higher, they would be of the < style.