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
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master

Details
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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(-)