[notmuch] date parser branch updated and rebased

[Sebastian Spaeth]

In order to not let this bitrot, I just rebased my dateparser branch to
current cworth master and split up the patches in a nicer way.
I made sure that every commit compiles. Let me know if there are things
that should be handled in a different way.

find the git branch here:
http://github.com/spaetz/notmuch-all-feature/commits/dateparser5

All 4 patches are going to be send as a reply to this mail in a second.

Sebastian