crash-recovery replay of CREATE TABLESPACE is broken in HEAD

I managed to crash the executor in the tablespace.sql test while working
on a 9.1 patch, and discovered that the postmaster fails to recover
from that.  The end of postmaster.log looks like

LOG:  all server processes terminated; reinitializing
LOG:  database system was interrupted; last known up at 2010-07-11 19:30:07 EDT
LOG:  database system was not properly shut down; automatic recovery in progress
LOG:  consistent recovery state reached at 0/EE26F30
LOG:  redo starts at 0/EE26F30
FATAL:  directory "/home/postgres/pgsql/src/test/regress/testtablespace/PG_9.1_201004261" already in use as a
tablespace
CONTEXT:  xlog redo create ts: 127158 "/home/postgres/pgsql/src/test/regress/testtablespace"
LOG:  startup process (PID 13914) exited with exit code 1
LOG:  aborting startup due to startup process failure

It looks to me like those well-intentioned recent changes in this area
broke the crash-recovery case.  Not good.
        regards, tom lane