ReadRecentBuffer() is broken for local buffer

ReadRecentBuffer() doesn't work for local buffers, i.e. for temp tables. 
The bug is pretty clear if you look at the code:

      if (BufferIsLocal(recent_buffer))
      {
-        bufHdr = GetBufferDescriptor(-recent_buffer - 1);
+        bufHdr = GetLocalBufferDescriptor(-recent_buffer - 1);

The code after that looks suspicious, too. It increases the usage count 
even if the buffer was already pinned. That's different from what it 
does for a shared buffer, and different from LocalBufferAlloc(). That's 
pretty harmless, just causes the usage count to be bumped more 
frequently, but I don't think it was intentional. The ordering of 
bumping the usage count, the local ref count, and registration in the 
resource owner are different too. As far as I can see, that makes no 
difference, but I think we should keep this code as close as possible to 
similar code used elsewhere, unless there's a particular reason to differ.

I propose the attached to fix those things.

I tested this by adding this little snippet to a random place where we 
have just read a page with ReadBuffer:

diff --git a/src/backend/access/heap/heapam.c 
b/src/backend/access/heap/heapam.c
index aab8d6fa4e5..c4abdbc96dd 100644
--- a/src/backend/access/heap/heapam.c
+++ b/src/backend/access/heap/heapam.c
@@ -403,6 +403,14 @@ heapgetpage(TableScanDesc sscan, BlockNumber page)
 
    RBM_NORMAL, scan->rs_strategy);
         scan->rs_cblock = page;

+       {
+               bool still_ok;
+
+               still_ok = 
ReadRecentBuffer(scan->rs_base.rs_rd->rd_locator, MAIN_FORKNUM, page, 
scan->rs_cbuf);
+               Assert(still_ok);
+               ReleaseBuffer(scan->rs_cbuf);
+       }
+
         if (!(scan->rs_base.rs_flags & SO_ALLOW_PAGEMODE))
                 return;

Without the fix, the assertion is fails quickly on "make check".

- Heikki