Proposal: new version of getModificationTime

[Felix Martini]

Hello all,

Function getModificationTime in System.Directory returns ClockTime.
ClockTime is part of the old-time package. The (new) time package has
UTCTime, so i propose a new version of getModificationTime that
returns UTCTime instead. I am not sure what a good name for the new
version would be, perhaps getModificationUTCTime?

Regards,
Felix