Feature request: Point in Time as a virtual dependency

Hi,

this is a feature request.

When declaring a filetask

file somefile => someother do
   do_something
end

it is executed only if either somefile does not exist, or one of the dependencies is newer.

But quite often I have requirements to not have a file get too old, which is not exactly straightforward in Rake.

Proposal:

Allow to define a point in Time to work as a virtual dependency, e.g. something like

d=DateTime.now.prev_month

file somefile => d do
  # recreate the file
end

to not let the File get older than the given date. Should be easy to implement.

regards

The issue names no files or tests. Start by locating Rake's file-task dependency handling and its existing timestamp comparison, then determine how a DateTime dependency would fit that model. Done should include defined behavior for the example and coverage for the point-in-time dependency.