Avoid unnecessary I/O to track files' 'last access' timestamp:

[nbougalis]

Unless the underlying filesystem is mounted with noatime then the system will keep track of and update a file's 'last access' time stamp with every read operation.

Even if the filesystem optimizes this, it makes little sense to track this information for NuDB files that can be accessed tens of thousands of times per second.

If the O_NOATIME option is defined, we set it when attempting to open or create files.

[vinniefalco]

yeah I agree