Add persistent reference list to manifest.

The reference list was previously built at load time from whichever references existed in the file list. This was sufficient since the list was for informational purposes only.

The block incremental feature will require a reference list that contains all prior backups, even those that are not explicitly referenced from the manifest. Therefore it makes sense to build and persist a manifest list rather than building it at load time.

This list can still be used for informational purposes, though it needs to be sorted since the list it sill built for older manifest versions and may not be in sorted order.

Add strLstFindIdx() to find references in the list.

test/src/module/command/backupTest.c

@@ -2547,6 +2547,7 @@ testRun(void)
             const String *resumeLabel = backupLabelCreate(
                 backupTypeDiff, manifestData(manifestPrior)->backupLabel, backupTimeStart);
             manifestBackupLabelSet(manifestResume, resumeLabel);
+            strLstAddZ(manifestResume->pub.referenceList, "BOGUS");
 
             // Reference in manifest
             HRN_STORAGE_PUT_EMPTY(storageRepoWrite(), zNewFmt(STORAGE_REPO_BACKUP "/%s/pg_data/PG_VERSION.gz", strZ(resumeLabel)));