Avoid using large buffers in 'string.format'

The result of "string.format("%.99f", -1e308) is 410 characters long,
but all other formats have much smaller limits (at most 99 plus a fex
extras). This commit avoids 'string.format' asking for a buffer
~400 chars large when ~100 will do.

luaconf.h

@@ -709,16 +709,9 @@
 
 /*
 @@ LUAL_BUFFERSIZE is the buffer size used by the lauxlib buffer system.
-** CHANGE it if it uses too much C-stack space. (For long double,
-** 'string.format("%.99f", -1e4932)' needs 5052 bytes, so a
-** 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)(16 * sizeof(void*) * sizeof(lua_Number)))
-#endif
+
 
 /*
 @@ LUAI_MAXALIGN defines fields that, when used in a union, ensure