Make homograph calculations consistent with entry sorting

As was already implemented in the 'fixup' code, we should treat
entry morphtypes as 'the same' for homograph purposes if they
have the same secondary sort order, rather than (as previously)
automatically considering several other types equivalent to stem
and all affixes distinct.

Change-Id: I55122da57b0d53911329e4fa6ec12261f24c42c3