[PATCH 0/5] Fetch all message metadata in a single pass

[Austin Clements]

This is the second of the two optimizations I described a while ago,
and brings my inbox search down to 1.811 seconds, 2.5X faster than it
was originally.

This optimization is based on the observation that Xapian decompresses
a document's term list every time you iterate over it.  As a result,
notmuch can decompress the beginning of a single term list quite a few
times.  This patch series combines all of this into a single pass that
is only slightly more expensive than fetching one metadata field used
to be, but offers a huge win in the common case where a message object
is used for multiple metadata fields.