fifo_buffer: add function fifo_buffer_realloc()

For growing FIFO buffers.

src/fifo_buffer.h

@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2003-2010 The Music Player Daemon Project
+ * Copyright (C) 2003-2011 The Music Player Daemon Project
  * http://www.musicpd.org
  *
  * Redistribution and use in source and binary forms, with or without
@@ -56,6 +56,18 @@ struct fifo_buffer;
 struct fifo_buffer *
 fifo_buffer_new(size_t size);
 
+/**
+ * Change the capacity of the #fifo_buffer, while preserving existing
+ * data.
+ *
+ * @param buffer the old buffer, may be NULL
+ * @param new_size the requested new size of the #fifo_buffer; must
+ * not be smaller than the data which is stored in the old buffer
+ * @return the new buffer, may be NULL if the requested new size is 0
+ */
+struct fifo_buffer *
+fifo_buffer_realloc(struct fifo_buffer *buffer, size_t new_size);
+
 /**
  * Frees the resources consumed by this #fifo_buffer object.
  */