Disable msgclass changing code for in Body Crypto

* src/mapihelp.cpp (get_msgcls_from_pgp_lines): Disable for
  Outlook >= 2010.

For now we want to ignore clearsigned and PGP/Inline
signed code as we still have the old body based interface
for those. And before we handle them we should tackle
some interoperability issues arising from our current
handling (e.g. fix the wipe to restore the PGP body)