fix #615

After setting the fuse.directio flag in cgofuse lib, I think the only thing left is to pass this flag to IRP_CREATE.Rsp.Create.Opened.DisableCache. To achieve that, I expanded the OPEN interface to accept a DisableCache pointer in this PR.

Another approach I considered is changing the parameter type from FSP_FSCTL_FILE_INFO *FileInfo to FSP_FSCTL_OPEN_FILE_INFO *, and then adding a DisableCache field into the FSP_FSCTL_OPEN_FILE_INFO struct.

Both methods seem fine to me. Do you think there is a better solution, or is there something I might have overlooked?

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