track exported files in a sqlite database

Went with a separate db per export remote, rather than a single export
database. Mostly because there will probably not be a lot of separate
export remotes, and it might be convenient to be able to delete a given
remote's export database.

This commit was supported by the NSF-funded DataLad project.

Annex/Locations.hs

@@ -36,6 +36,7 @@ module Annex.Locations (
 	gitAnnexFsckDbDir,
 	gitAnnexFsckDbLock,
 	gitAnnexFsckResultsLog,
+	gitAnnexExportDbDir,
 	gitAnnexScheduleState,
 	gitAnnexTransferDir,
 	gitAnnexCredsDir,
@@ -290,6 +291,15 @@ gitAnnexFsckDbLock u r = gitAnnexFsckDir u r </> "fsck.lck"
 gitAnnexFsckResultsLog :: UUID -> Git.Repo -> FilePath
 gitAnnexFsckResultsLog u r = gitAnnexDir r </> "fsckresults" </> fromUUID u
 
+{- .git/annex/export/uuid/ is used to store information about
+ - exports to special remotes. -}
+gitAnnexExportDir :: UUID -> Git.Repo -> FilePath
+gitAnnexExportDir u r = gitAnnexDir r </> "export" </> fromUUID u
+
+{- Directory containing database used to record export info. -}
+gitAnnexExportDbDir :: UUID -> Git.Repo -> FilePath
+gitAnnexExportDbDir u r = gitAnnexExportDir u r </> "db"
+
 {- .git/annex/schedulestate is used to store information about when
  - scheduled jobs were last run. -}
 gitAnnexScheduleState :: Git.Repo -> FilePath