detected during buffer dump to be labeled with the buffer location.
For example, if a page LSN is clobbered, we now produce something like
ERROR:  XLogFlush: request 2C000000/8468EC8 is not satisfied --- flushed only
to 0/8468EF0
CONTEXT:  writing block 0 of relation 428946/566240
whereas before there was no convenient way to find out which page had
been trashed.