[Review] Request from 'schubi2' @ 'yast/yast-autoinstallation/review_140806_export_deleted_package_selection'

Please review the following changes:
  * da63299 packaging
  * 4d4ec19 export removed packages correctly

The complex selection condition occurs 1 other time in this file, in `read_initial_stage`. Maybe it could be factored out. 
Also, `package["locked"]` is a boolean* so `== true` is redundant. 

\*) source:
https://github.com/yast/yast-pkg-bindings/blob/2128a6c31d80c73c5d981df49b9108c2f70c55f1/src/Resolvable_Properties.cc#L225
@lslezak , is there HTML docs for Pkg::*?