add config validation for Windows config
Merge pull request #1275 from markbenvenuto/win_config_validate

add config validation for Windows config
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Update.
It's an error if we don't find build_win/wiredtiger_config.h.
Fix Windows os_dir.c, and os_ftruncate.c. Correctly enable hardware chksum.
Merge pull request #1276 from markbenvenuto/dir_fix

Fix Windows os_dir.c, and os_ftruncate.c. Correctly enable hardware chksum
KNF
Put a tags file into the Windows directory.
FindFirstFile returns INVALID_HANDLE_VALUE, not NULL