Added gcc option '-Wconversion'

No warnings for standard numerical types. Still pending alternative
numerical types.

llimits.h

@@ -130,6 +130,7 @@ typedef LUAI_UACINT l_uacInt;
 #define cast_num(i)	cast(lua_Number, (i))
 #define cast_int(i)	cast(int, (i))
 #define cast_uint(i)	cast(unsigned int, (i))
+#define cast_ulong(i)	cast(unsigned long, (i))
 #define cast_byte(i)	cast(lu_byte, (i))
 #define cast_uchar(i)	cast(unsigned char, (i))
 #define cast_char(i)	cast(char, (i))
@@ -151,6 +152,16 @@ typedef LUAI_UACINT l_uacInt;
 #define l_castU2S(i)	((lua_Integer)(i))
 #endif
 
+/*
+** cast a size_t to lua_Integer: These casts are always valid for
+** sizes of Lua objects (see MAX_SIZE)
+*/
+#define cast_st2S(sz)	((lua_Integer)(sz))
+
+/* Cast a ptrdiff_t to size_t, when it is known that the minuend
+** comes from the subtraend (the base)
+*/
+#define ct_diff2sz(df)	((size_t)(df))
 
 /*
 ** Special type equivalent to '(void*)' for functions (to suppress some