When EasyPG is enabled, multipart/signed and application/pkcs7-mime
enveloped messages are properly handled.

However, application/pkcs7-mime messages of type signed (aka "opaque
signed") are passed off to smime-verify-region, which is incorrect.

This also happens with messages that are signed and encrypted, in that
case the outer envelope is properly handled, but the inner message is of
type application/pkcs7-mime signed, which then follows the same from
through mm-view-pkcs7.

Backtrace below, sample message attached.