stand: liblua: drop default buffer size to 128

Lua allocates LUAL_BUFFERSIZE buffers on the stack for various string
functions (string.format, string.gsub) -- this works out to be somewhat
significant and not necessary, based on how we use string operations.
Dropping it risks having to allocate per call to format/gsub, but this is
not the case for our usage. This simply stops allocating 8K buffers on the
stack when luaL_Buffer is used.

Reviewed by:	imp
MFC after:	1 week
Differential Revision:	https://reviews.freebsd.org/D22500

stand/liblua/luaconf.h

@@ -783,11 +783,7 @@
 ** smaller buffer would force a memory allocation for each call to
 ** 'string.format'.)
 */
-#if LUA_FLOAT_TYPE == LUA_FLOAT_LONGDOUBLE
-#define LUAL_BUFFERSIZE		8192
-#else
-#define LUAL_BUFFERSIZE   ((int)(0x80 * sizeof(void*) * sizeof(lua_Integer)))
-#endif
+#define LUAL_BUFFERSIZE		128
 
 /* }================================================================== */