Only transform hashes to Hash::AsObject objects, leave other structures alone

... since Hash::AsObject doesn't support them and throws warnings
during global destruction.

This can be verified by running "wu" with "perl -w" enabled:

        $ perl -w -S wu
        Enter city or zip / postal code (New York City, NY): 94114
        ...
	(in cleanup) Not a HASH reference at /Users/mschilli/perl5/lib/perl5/Hash/AsObject.pm line 102.

(there's a few other warnings still unfixed with Cache/FileBackend.pm, I'll leave that for another day).