BUG: already mixed indexes should not sort

[cpcloud]

cc @jreback

[jreback]

passes for me

[cpcloud]

Yeah but not passing on Travis :(

[cpcloud]

Some tuple edge case

[cpcloud]

@jreback can u take a look here? previously this was sorting (since tuples are sortable), then comparing against a MultiIndex. So this is a breaking API change, albeit for non MultiIndex tuple Indexes, which are rare.

[cpcloud]

the change is that sorting mixed dtype indexes doesn't work for any objects, including things that do have an ordering.

[cpcloud]

@jreback ok with this?

[jreback]

seems ok, I don't really understand what its supposed to do. doubt this is really an issue in practice (except the error of course!) so ok

[cpcloud]

tuples have an ordering which means they can be sorted inplace no problem, but i check for mixed and mixed-integer inferred_type which tuples satisfy. i thought it was better to not sort anything that's mixed, than to special case tuples