MEDIUM: chunk: Add support for large chunks

MEDIUM: chunk: Add support for large chunks

Because there is now a memory pool for large buffers, we must also add the
support for large chunks. So, if large buffers are configured, a dedicated
memory pool is created to allocate large chunks. alloc_large_trash_chunk()
must be used to allocate a large chunk. alloc_trash_chunk_sz() can be used to
allocate a chunk with the best size. However free_trash_chunk() remains the
only way to release a chunk, regular or large.

In addition, large trash buffers are also created, using the same mechanism
than for regular trash buffers. So three thread-local trash buffers are
created. get_large_trash_chunk() must be used to get a large trash buffer.
And get_trash_chunk_sz() may be used to get a trash buffer with the best
size.