[crush] Add Lua version compatibility check.

crush.lua

@@ -7,6 +7,33 @@
 local io = require 'io'
 local os = require 'os'
 
+-- Lua version check
+
+local function check_version()
+    -- Generic Lua version check - 5.2 required
+    if _VERSION then
+        local maj, min = _VERSION:match("Lua (%d+)%.(%d+)")
+
+        if maj and min then
+            maj, min = tonumber(maj), tonumber(min)
+            if maj > 5 or (maj == 5 and min >= 2) then
+                return true
+            end
+        end
+    end
+
+    -- LuaJIT check - 2.0.0 required (technically 2.0.0_beta11)
+    if jit and jit.version_num and jit.version_num >= 20000 then
+        return true
+    end
+
+    return false
+end
+
+if not check_version() then
+    error("Unsupported Lua version!\nSorry, crush requires Lua 5.2 or LuaJIT 2.0.0.")
+end
+
 -- System specific functions
 --
 -- Portions of this code are based on work from the LuaRocks project.