pgsql: Suppress timezone (%Z) part of timestamp display when running on

Log Message:
-----------
Suppress timezone (%Z) part of timestamp display when running on Windows,
because on that platform strftime produces localized zone names in varying
encodings. Even though it's only in a comment, this can cause encoding
errors when reloading the dump script. Per suggestion from Andreas
Seltenreich. Also, suppress %Z on Windows in the %s escape of
log_line_prefix ... not sure why this one is different from the other two,
but it shouldn't be.

Modified Files:
--------------
pgsql/src/backend/utils/error:
elog.c (r1.176 -> r1.177)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/backend/utils/error/elog.c.diff?r1=1.176&r2=1.177)
pgsql/src/bin/pg_dump:
pg_backup_archiver.c (r1.137 -> r1.138)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_backup_archiver.c.diff?r1=1.137&r2=1.138)
pg_dumpall.c (r1.84 -> r1.85)
(http://developer.postgresql.org/cvsweb.cgi/pgsql/src/bin/pg_dump/pg_dumpall.c.diff?r1=1.84&r2=1.85)