Basically, custom partitioning does a storage check before you leave.
However,
there's no chance to set a passphrase before leaving. Thus if the user
chooses encryption, they will always get an error before they can set the
passphrase in question.
This allows skipping the check, which should be fine for anaconda since there's
no way out custom partitioning without hitting the passphrase dialog.
Related: rhbz#1060255
Ignore these two. mulhern has a better approach in the works.
- Chris