pgsql: Use correct path separator for Windows builtin commands.

Use correct path separator for Windows builtin commands.

pg_upgrade produces a platform-specific script to remove the old
directory, but on Windows it has not been making sure that the
paths it writes as arguments for rmdir and del use the backslash
path separator, which will cause these scripts to fail.

The fix is backpatched to Release 9.0.

Branch
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master

Details
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http://git.postgresql.org/pg/commitdiff/504aeea6926730f6fa9d3e0ec3a181b659c2f594

Modified Files
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contrib/pg_upgrade/check.c      |   47 +++++++++++++++++++++++++++++++++-----
contrib/pg_upgrade/pg_upgrade.h |    2 +
2 files changed, 42 insertions(+), 7 deletions(-)