Allow postponing to a different milestone

[Martin Pitt]

Related to bug 509805, we should introduce a new syntax

  description: POSTPONED to milestonename

with the following semantics:

 * for the milestone which the WI is originally reported under, it counts as "postponed"

 * for the "milestonename" milestone it counts as "todo"

for closing that WI there is currently no straightforward syntax. I propose that the WI gets copied to the new milestone section with status "done". The report engine already ensures that work items with identical descriptions are just counted once.

[Robbie Williamson (robbiew)]

+1 for me

[Jamie Bennett (jamiebennett)]

For a simpler implementation, this could be done with a LATER status. If the tracker comes across a LATER status it assumes that the same work item will appear later in the white board and thus does not count it in the metrics. Of course from just a LATER status you can't determine where the work item was POSTPONED _to_ but it at least it leaves the whiteboard intact for the interested to go back and figure that detail out themselves.

[Jamie Bennett (jamiebennett)]

Linking in an implementation as adding a new state requires an ack from the maintainers IMHO.

[Martin Pitt (pitti)]

I'm not quite convinced about the need of a new status here, and if possible, I'd like to avoid inflating the number of states even more. Let's discuss this in the MP. Thanks!