Improve json_object -> string performance

Removes variadic prints for ~3x performance improvement.

printbuf.c

@@ -85,6 +85,7 @@ int printbuf_memappend(struct printbuf *p, const char *buf, int size)
     if (printbuf_extend(p, p->bpos + size + 1) < 0)
       return -1;
   }
+
   memcpy(p->buf + p->bpos, buf, size);
   p->bpos += size;
   p->buf[p->bpos]= '\0';
@@ -111,34 +112,6 @@ int printbuf_memset(struct printbuf *pb, int offset, int charvalue, int len)
 	return 0;
 }
 
-int sprintbuf(struct printbuf *p, const char *msg, ...)
-{
-  va_list ap;
-  char *t;
-  int size;
-  char buf[128];
-
-  /* user stack buffer first */
-  va_start(ap, msg);
-  size = vsnprintf(buf, 128, msg, ap);
-  va_end(ap);
-  /* if string is greater than stack buffer, then use dynamic string
-     with vasprintf.  Note: some implementation of vsnprintf return -1
-     if output is truncated whereas some return the number of bytes that
-     would have been written - this code handles both cases. */
-  if(size == -1 || size > 127) {
-    va_start(ap, msg);
-    if((size = vasprintf(&t, msg, ap)) < 0) { va_end(ap); return -1; }
-    va_end(ap);
-    printbuf_memappend(p, t, size);
-    free(t);
-    return size;
-  } else {
-    printbuf_memappend(p, buf, size);
-    return size;
-  }
-}
-
 void printbuf_reset(struct printbuf *p)
 {
   p->buf[0] = '\0';
@@ -152,3 +125,8 @@ void printbuf_free(struct printbuf *p)
     free(p);
   }
 }
+
+inline int sprintbuf(struct printbuf *p, const char *buf)
+{
+  return printbuf_memappend(p, buf, strlen(buf));
+}