Fix: test_src -eaux plurals

These plurals (e.g. "gateau" -> "gateaux") were added to makeplural and
makesingular in 0c0262e, so the test was outdated and failed.  I also
added another test for "Federal Bureau of Investigation", since 'bureau'
is an exception to the -eau rule (pluralizes as 'bureaus') and the
exception was originally implemented in a way that would have caused the
"Federal Bureau of Investigation" test to fail -- so it seems like a
good pitfall to test for.

test/test_src.lua

@@ -6,7 +6,7 @@ local tests = {
       algae = "algae",
       amoeba = "amoebae",
       baluchitherium = "baluchitheria",
-      bordeau = "bordeaus",
+      Bordeaux = "Bordeaux",
       ["bunch of grapes"] = "bunches of grapes",
       bus = "buses",
       candelabrum = "candelabra",
@@ -16,12 +16,12 @@ local tests = {
       deer = "deer",
       dingo = "dingoes",
       epoch = "epochs",
+      ["Federal Bureau of Investigation"] = "Federal Bureaus of Investigation",
       fish = "fish",
       foot = "feet",
       fox = "foxes",
       fungus = "fungi",
-      gateau = "gateaus",
+      gateau = "gateaux",
-      gateaux = "gateauxes",
       gauntlet = "gauntlets",
       ["gauntlet of power"] = "gauntlets of power",
       goose = "geese",