+Save filenames for files detected as "not an email file" in the
+database. This would allow for two things: 1. Optimizing "notmuch new"
+to not have to look at these files again (since they are potentially
+large so the detection could be potentially slow). 2. A "notmuch
+search" syntax could be added to allow the user to find these files,
+(and perhaps delete them or move them away as appropriate).
+
+Fix filesystem/notmuch-new race condition by not updating database
+mtime for a directory if it is the same as the current mtime.
+