Fix sscsm.get_player_control() on MT 5.4.0-dev.

This further bloats sscsm_init.lua to ensure the LMB/RMB fields are 
equal to dig/place.

README.md

@@ -130,6 +130,8 @@ SSCSMs can access most functions on [client_lua_api.txt](https://github.com/mine
  - `sscsm.get_player_control()`: Alternative for
     `minetest.localplayer:get_control()` that works with Minetest 5.2.0 and
     below.
+    - The `LMB` and `RMB` fields are deprecated and will probably be removed in
+      the future, use `dig` and `place` instead.
  - `sscsm.every(interval, func, ...)`: Calls `func` every `interval` seconds
     with any extra parameters specified. Use `minetest.register_globalstep`
     instead if `interval` is `0`.

sscsm_init.lua

@@ -133,22 +133,39 @@ end
 
 -- A proper get_player_control didn't exist before Minetest 5.3.0.
 if minetest.localplayer.get_control then
+    -- Preserve API compatibility
+    if minetest.localplayer:get_control().LMB == nil then
+        -- MT 5.4+
         function sscsm.get_player_control()
-        return minetest.localplayer:get_control()
+            local c = minetest.localplayer:get_control()
+            c.LMB, c.RMB = c.dig, c.place
+            return c
+        end
+    else
+        -- MT 5.3
+        function sscsm.get_player_control()
+            local c = minetest.localplayer:get_control()
+            c.dig, c.place = c.LMB, c.RMB
+            return c
+        end
     end
 else
+    -- MT 5.0 to 5.2
+    local floor = math.floor
     function sscsm.get_player_control()
         local n = minetest.localplayer:get_key_pressed()
         return {
             up    = n % 2 == 1,
-            down  = math.floor(n / 2) % 2 == 1,
-            left  = math.floor(n / 4) % 2 == 1,
-            right = math.floor(n / 8) % 2 == 1,
-            jump  = math.floor(n / 16) % 2 == 1,
-            aux1  = math.floor(n / 32) % 2 == 1,
-            sneak = math.floor(n / 64) % 2 == 1,
-            LMB   = math.floor(n / 128) % 2 == 1,
-            RMB   = math.floor(n / 256) % 2 == 1,
+            down  = floor(n / 2) % 2 == 1,
+            left  = floor(n / 4) % 2 == 1,
+            right = floor(n / 8) % 2 == 1,
+            jump  = floor(n / 16) % 2 == 1,
+            aux1  = floor(n / 32) % 2 == 1,
+            sneak = floor(n / 64) % 2 == 1,
+            LMB   = floor(n / 128) % 2 == 1,
+            RMB   = floor(n / 256) % 2 == 1,
+            dig   = floor(n / 128) % 2 == 1,
+            place = floor(n / 256) % 2 == 1,
         }
     end