pgsql: Properly check for readdir/closedir() failures

Properly check for readdir/closedir() failures

Clear errno before calling readdir() and handle old MinGW errno bug
while adding full test coverage for readdir/closedir failures.

Backpatch through 8.4.

Branch
------
master

Details
-------
http://git.postgresql.org/pg/commitdiff/6f03927fce038096f53ca67eeab9adb24938f8a6

Modified Files
--------------
contrib/pg_archivecleanup/pg_archivecleanup.c |   16 ++++++-
contrib/pg_standby/pg_standby.c               |   17 +++++++-
src/backend/storage/file/fd.c                 |    5 +--
src/bin/initdb/initdb.c                       |   12 +++---
src/bin/pg_basebackup/pg_receivexlog.c        |   22 +++++++++-
src/bin/pg_dump/pg_backup_directory.c         |   17 +++++++-
src/bin/pg_resetxlog/pg_resetxlog.c           |   57 +++++++++++++------------
src/common/pgfnames.c                         |   19 +++++----
src/port/dirent.c                             |    8 +++-
src/port/pgcheckdir.c                         |   14 ++----
10 files changed, 122 insertions(+), 65 deletions(-)