win32 inode fix

For community review and application to HEAD; minor patch.

Under Win32, stat() returns an st_ino field, but it has no meaning (on
Win2K, and possibly all Win32 variants, it is always 0). This causes a
number of problems in the dfmgr.c logic, which basically all revolve around
the fact that *any* two files will appear to have the same inode.

Note also that this solves the current issues related to initdb under Win32.

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