only use writev for larger chunks in buffer_putflush

only use lseek if it saves a read in buffer_seek

buffer/buffer_putflush.c

@@ -22,7 +22,7 @@ int buffer_putflush(buffer* b,const char* x,size_t len) {
   if (!b->p)	/* if the buffer is empty, just call buffer_stubborn directly */
     return buffer_stubborn(b->op,b->fd,x,len,b);
 #ifndef __MINGW32__
-  if (b->op==write) {
+  if (b->op==write && len>sizeof(struct iovec)*2) {
     struct iovec v[2];
     ssize_t w;
     size_t cl=b->p+len;

buffer/buffer_seek.c

@@ -17,8 +17,9 @@ ssize_t buffer_seek(buffer* b,size_t len) {
     len -= leftinbuf;
     b->p = 0;	// clear buffer
     b->n = 0;
+
     /* change position in underlying file */
-    if (b->fd != -1 &&
+    if (b->fd != -1 && len > b->a &&
         lseek(b->fd, len, SEEK_CUR) != -1) return len;
     // either we have no fd or input is not seekable
     // call read repeatedly