TestAccount used two local state keys per app. With two keys sort.Slice
does a single compare-and-swap, so the test passed while the sort was
broken. A third key makes the test fail on the old code.

convertTKVToGenerated sorted the converted entries with a comparator that
indexed a parallel slice of raw keys. sort.Slice swaps only the slice it
sorts, so the comparator read stale keys and the output order changed
from request to request. Iterate the map in sorted key order instead.