Tie in new MFHD method to serials module/MFHD tests for compressing, combining

Tie in new MFHD method to serials module/MFHD tests for compressing, combining

[This commit has been squashed for merging. LFW]

 *  Now that we have a potentially better alternative, let's call
    get_combined_holdings() in place of get_compressed_holdings() in
    Serial.pm.

 *  First, add a test for the new get_combined_holdings() method.

    Second, add a known problem case for get_compressed_holdings().
    The fix will come in a subsequent commit.

Signed-off-by: Dan Wells <dbw2@calvin.edu>
Signed-off-by: Lebbeous Fogle-Weekley <lebbeous@esilibrary.com>