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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REL9_2_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/ee42d8f10b65593aab768438665000aec070f6c2

Modified Files
--------------
contrib/pg_archivecleanup/pg_archivecleanup.c | 16 ++++++-
contrib/pg_standby/pg_standby.c | 17 ++++++-
contrib/pg_upgrade/file.c | 9 ++--
src/backend/storage/file/fd.c | 6 +--
src/bin/pg_basebackup/pg_receivexlog.c | 22 ++++++++-
src/bin/pg_resetxlog/pg_resetxlog.c | 63 +++++++++++++------------
src/port/dirent.c | 8 +++-
src/port/dirmod.c | 22 +++++----
src/port/pgcheckdir.c | 14 ++----
9 files changed, 109 insertions(+), 68 deletions(-)