Changed the growth rate of string buffers

The growth rate of string buffers was reduced from 2 to 1.5 (3/2).
As string buffers start larger (256~1024 bytes), they don't need to
grow that fast. Moreover, a lower rate allows multiplicative growth up
to larger sizes (3/2 of the maximum). (After that, the growth becomes
linear, which is mostly useless.)

lauxlib.c

@@ -526,14 +526,14 @@ static void newbox (lua_State *L) {
 
 /*
 ** Compute new size for buffer 'B', enough to accommodate extra 'sz'
-** bytes. (The test for "double is not big enough" also gets the
-** case when the multiplication by 2 overflows.)
+** bytes. (The test for "not big enough" also gets the case when the
+** computation of 'newsize' overflows.)
 */
 static size_t newbuffsize (luaL_Buffer *B, size_t sz) {
-  size_t newsize = B->size * 2;  /* double buffer size */
+  size_t newsize = (B->size / 2) * 3;  /* buffer size * 1.5 */
   if (l_unlikely(MAX_SIZET - sz < B->n))  /* overflow in (B->n + sz)? */
     return luaL_error(B->L, "buffer too large");
-  if (newsize < B->n + sz)  /* double is not big enough? */
+  if (newsize < B->n + sz)  /* not big enough? */
     newsize = B->n + sz;
   return newsize;
 }

luaconf.h

@@ -747,14 +747,15 @@
 
 /*
 @@ LUA_IDSIZE gives the maximum size for the description of the source
-@@ of a function in debug information.
+** of a function in debug information.
 ** CHANGE it if you want a different size.
 */
 #define LUA_IDSIZE	60
 
 
 /*
-@@ LUAL_BUFFERSIZE is the buffer size used by the lauxlib buffer system.
+@@ LUAL_BUFFERSIZE is the initial buffer size used by the lauxlib
+** buffer system.
 */
 #define LUAL_BUFFERSIZE   ((int)(16 * sizeof(void*) * sizeof(lua_Number)))