Add retaining walls

Fixes #61

barrier.lua

@@ -8,7 +8,10 @@ This file is part of ClearTables
 require "common"
 
 function accept_barrier_line (tags)
-    return tags["barrier"] == "fence" or tags["barrier"] == "wall" or tags["barrier"] == "hedge"
+    return tags["barrier"] == "fence" or
+           tags["barrier"] == "wall" or
+           tags["barrier"] == "hedge" or
+           tags["barrier"] == "retaining_wall"
 end
 
 function transform_barrier_line (tags)

test-barrier.lua

@@ -14,11 +14,13 @@ assert(not accept_barrier_line({foo="bar"}), "test failed: other tags")
 assert(accept_barrier_line({barrier="fence"}), "test failed: barrier=fence")
 assert(accept_barrier_line({barrier="wall"}), "test failed: barrier=wall")
 assert(accept_barrier_line({barrier="hedge"}), "test failed: barrier=hedge")
+assert(accept_barrier_line({barrier="retaining_wall"}), "test failed: barrier=retaining_wall")
 assert(not accept_barrier_line({barrier="foo"}), "test failed: other barrier")
 
 print("TESTING: transform_barrier_line")
 assert(deepcompare(transform_barrier_line({}), {}), "test failed: no tags")
 assert(transform_barrier_line({barrier="fence"}).barrier == "fence", "test failed: fence")
 assert(transform_barrier_line({barrier="wall"}).barrier == "wall", "test failed: wall")
 assert(transform_barrier_line({barrier="hedge"}).barrier == "hedge", "test failed: hedge")
+assert(transform_barrier_line({barrier="retaining_wall"}).barrier == "retaining_wall", "test failed: retaining_wall")
 assert(transform_barrier_line({height="5"}).height == "5", "test failed: height")