svnadmin dump files are not reproducible, due to APR 1.4.6 hash order changes

APR 1.4.6 made the iteration order of hashes non-reproducible between runs (and
for good reasons).  This broke several dozen tests[1], among them those that
test 'svnadmin dump''s output[2].

This issue calls for having 'svnadmin dump' produce the same output when run twice.


[1] see r1293811, r1293602 on ^/subversion/branches/1.7.x
[2] see r1292507 on trunk/.