Some tweaks to mine.lua.

- Checks for movement success now, tries to ensure movement even if a block
  falls in front of the turtle.
- Fixed the bug for depths of 1 mod 3 leaving a plane of blocks.

mine.lua

@@ -30,10 +30,12 @@ function moveInLine (delta)
         if mode.mine.forward then
             turtle.dig()
         end
-        turtle.forward()
+        local success = turtle.forward()
+        if success then
             mineSides()
             delta = delta - 1
         end
+    end
 end
 
 function moveUpDown (delta)
@@ -42,16 +44,20 @@ function moveUpDown (delta)
         if mode.mine.forward then
             turtle.digUp()
         end
-        turtle.up()
+        local success = turtle.up()
+        if success then
             delta = delta - 1
         end
+    end
     while delta < 0 do
         if mode.mine.forward then
             turtle.digDown()
         end
-        turtle.down()
+        local success = turtle.down()
+        if success then
             delta = delta + 1
         end
+    end
 end
 
 function turnToFace (new_direction)
@@ -206,6 +212,9 @@ function mine (block)
     local excess = remaining_h % 3
     if excess > 0 then
         minePlane(block.xoff, block.yoff, (excess - 1) * z_dir)
+        if excess == 1 then
+            move(0, 0, -z_dir)
+        end
         remaining_h = remaining_h - excess
     else
         move(0, 0, z_dir)