Get road connections working, and convert grass/hill road crossings from old scenarios

In classic BoE, to make a road cross the boundary of grass and hills, you would place a "road on hill" terrain where the boundary should be, and the game would automatically convert it to the correct type of boundary before drawing the road on top. Now, the game expects you to place the proper boundary there instead, meaning there is some more complicated logic to determine when it needs to draw a road across a boundary, or, in some cases, two consecutive boundaries. It works for the surface world of Valley of the Dying Things; there may still be some edge cases that need fixing.

osx/boe.locutils.cpp

@@ -561,6 +561,7 @@ bool impassable(ter_num_t terrain_to_check)
 	else return false;
 }
 
+// TODO: What on earth is this and why does it mangle the blockage?
 short get_blockage(ter_num_t terrain_type)
 {
 	// little kludgy in here for pits
@@ -701,7 +702,7 @@ location push_loc(location from_where,location to_where)
 }
 
 
-
+// TODO: This seems to be wrong; aren't 3 and 4 also impassable?
 bool spot_impassable(short i,short  j)
 {
 	ter_num_t ter;