try using native bitwise operations without checking lua version

http/bit.lua

@@ -7,17 +7,26 @@ The bit operations are only done
 This means we can ignore the differences between bit libraries.
 ]]
 
--- Lua 5.3 has built-in bit operators, wrap them in a function.
-if _VERSION == "Lua 5.3" then
-	-- Use debug.getinfo to get correct file+line numbers for loaded snippet
-	local info = debug.getinfo(1, "Sl")
-	return assert(load(("\n"):rep(info.currentline+1)..[[return {
-		band = function(a, b) return a & b end;
-		bor = function(a, b) return a | b end;
-		bxor = function(a, b) return a ~ b end;
-	}]], info.source))()
+-- Lua 5.1's load function doesn't support reading strings, only
+-- functions.
+local function string_loader(str)
+	local sent = false
+	return function()
+		if sent then return nil end
+		sent = false
+		return str
+	end
 end
 
+-- Lua 5.3+ has built-in bit operators, wrap them in a function.
+local info = debug.getinfo(1, "Sl")
+local has_bitwise, bitwise = pcall(load(string_loader(("\n"):rep(info.currentline+1)..[[return {
+	band = function(a, b) return a & b end;
+	bor = function(a, b) return a | b end;
+	bxor = function(a, b) return a ~ b end;
+}]]), info.source))
+if has_bitwise then return bitwise end
+
 -- The "bit" library that comes with luajit
 -- also available for lua 5.1 as "luabitop": http://bitop.luajit.org/
 local has_bit, bit = pcall(require, "bit")