[bug fix] PostgreSQL fails to start on Windows if it crashes after tablespace creation

Hello,

I've found and fixed a bug that causes recovery (crash recovery, PITR) to
fail. Please find attached the patch against HEAD.

[Bug]
To reproduce the problem, do the following on Windows:

1. pg_ctl start
2. CREATE TABLESPACE tbs LOCATION 'some_tblspc_path';
3. pg_ctl stop -mi
4. pg_ctl start

The database server fails to start, leaving the below messages:

LOG: database system was interrupted; last known up at 2013-10-31 20:24:07
JST
LOG: database system was not properly shut down; automatic recovery in
progress
LOG: redo starts at 0/1788938
FATAL: could not remove symbolic link "pg_tblspc/16385": Permission denied
CONTEXT: xlog redo create tablespace: 16385 "d:/tbs"
LOG: startup process (PID 2724) exited with exit code 1
LOG: aborting startup due to startup process failure

[Cause]
In redo, create_tablespace_directories() tries to remove the symbolic link
for the tablespace using unlink(). However, unlink() on Windows fails with
errno=13 (Permission denied). This is because junction points are
directories on Windows.

[Fix]
Follow destroy_tablespace_directories() and use rmdir() to remove the
junction point.

I've tested the patch. Could you review it and commit? I wish it to be
backported to all major releases.

Regards
MauMau