auto_select optional, default to True, unless `select` was explicitly specified

[josiahjohnston]

This is an incremental step towards streamlining the load_aug interface. Several modules still relied on explicitly using select, and changing those & upgrading inputs would have been a bigger can of worms.

[mfripp]

I ended up dropping the auto_select argument to load_aug entirely, since it no longer has a useful purpose. For now, users will just get a warning message if they try to use auto_select or autoselect.