Proposal: better timestamp granularity for modificationTime/setFileTimes in System.Posix.Files[.ByteString]

Dear all, System.Posix.Files[.ByteString] contains the following functions related to file times: accessTime, modificationTime, statusChangeTime, setFileTimes. All of these functions offer granularity of one second. Modern posix systems support newer functions (such as utimes, utimensat) that offer better granularity (up to 1 nanosecond). I propose to add a new set of functions to System.Posix.Files[.ByteString] to utilize these new capabilities. One problem here is the choice of the data type to be used for these timestamps as the EpochTime type only allows granularity of one second. One option might be POSIXTime from Data.Time.Clock.POSIX. I am willing to provide patches.