don't store the output density anymore. I now read it from the
last input density. ...this may be slightly inconsistent but
in the case of self convergence it should be irrelevant.

...it is used with the command line option -last_extra.

...not fully tested yet.

Note: This seems to have introduced some bugs. ...to be corrected soon.

...this surely is not yet the final version.

...there was a missing initialization if no cdn.hdf file was used.

Note: Also in this commit:

1. Changed test values in NiO_ldauXML test since now the broyden files get deleted
   when a new density matrix is generated
2. The NiO_ldau test should not work any more since linear mixing for the density
   matrix is removed for the old inp file. (It is not specified in the n_mmp_mat
   file any more)

Note: Two changes have been done in global/types.F90:

   1. MERGE(jsp,4,l_noco) -> MERGE(4,jsp,l_noco)
      (I think the new code is correcter. This change is required)

   2. Some dimension variable was replaced by stars%ng2.
      (Maybe this is not required and maybe the previous variable was more correct.)

It can be deactivated by using the command line switch -no_cdn_hdf