Deprecated the emulation of '__le' using '__lt'

As hinted in the manual for Lua 5.3, the emulation of the metamethod
for '__le' using '__le' has been deprecated. It is slow, complicates
the logic, and it is easy to avoid this emulation by defining a proper
'__le' function.

Moreover, often this emulation was used wrongly, with a programmer
assuming that an order is total when it is not (e.g., NaN in
floating-point numbers).

luaconf.h

@@ -295,7 +295,7 @@
 */
 
 /*
-@@ LUA_COMPAT_5_3 controls other macros for compatibility with Lua 5.2.
+@@ LUA_COMPAT_5_3 controls other macros for compatibility with Lua 5.3.
 ** You can define it to get all options, or change specific options
 ** to fit your specific needs.
 */
@@ -316,6 +316,12 @@
 */
 #define LUA_COMPAT_APIINTCASTS
 
+/*
+@@ LUA_COMPAT_LT_LE controls the emulation of the '__le' metamethod
+** using '__lt'.
+*/
+#define LUA_COMPAT_LT_LE
+
 #endif				/* } */