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).

ltests.h

@@ -13,6 +13,7 @@
 
 /* test Lua with compatibility code */
 #define LUA_COMPAT_MATHLIB
+#define LUA_COMPAT_LT_LE
 
 
 #define LUA_DEBUG