fixed normalize_get logic for unhandled LS_BUCKET case

fakes3 would think that an LS_BUCKET command was a LIST_BUCKETS command and never return the contents of buckets.
Format Last-Modified header as httpdate.
Added modified_http_date function to S3Object.
Fixed incorrect formatting of LastModified field in bucket listing.
Fixed normalize_get for bucket listing request.
Merge commit '7bfc57ede19466d6b6be489b30557be7d6f610f7'
Merge commit '613866e1ce9199b2e5c3e2507b88b2a96a755486'