(i_type, I_NONE): shift the enum down 1, so that I_NONE does not need to

(i_type, I_NONE): shift the enum down 1, so that I_NONE does not need to
be skipped or stored in arrays of size I_MAX. I_NONE's int equivalent
becomes -1 by this patch, so all array indices of type i_type have been
checked not to use I_NONE as index.  This change reduces the size of the
arrays stored in files.