PDOS xml file compatibility issues

[albgar]

Currently Siesta produces two PDOS files in XML:

• SystemLabel.PDOS is created by simple fortran write statements, and the relevant data is mostly in separate lines. This has traditionally made it useful for some third-party utilities such as Andrei Postnikov's post-processor.
• SystemLabel.PDOS.xml is created by calls to the wxml module of xmlf90. It is more compact, and the code to generate it is simpler. However, due to an oversight, it is missing the 'norbitals' element. Otherwise its data content is the same as that of the PDOS file.

We do not like to have to maintain two different files, so we are planning to deprecate the PDOS file. This has consequences for the PDOS support in the plugin. To maintain compatibility with all versions of Siesta:

• One should maybe check for the existence of both PDOS and PDOS.xml.
• If the 'norbitals' element is not found, the value of n_orbitals can be simply inferred by counting the number of 'orbital' elements in the file.