Luckily doable with much simpler code than the horrible NSS and curl mess used
on Linux (and, sadly, OS X).

Basically only one new API call needed: CryptRetrieveTimestamp(). A few hours
of work, compared to about a week for the Linux case.

However, amusingly, it causes the same message in Adobe Reader as when using
the NSS code: "The signature includes an embedded timestamp but it could not
be verified". Sigh.

Change-Id: I98c973bd50b841d1ae3feb8a695bac29da538b6c