uses CORES global variable
fixed data errors
 - found duplicate issues in source data
 - wrote acd drops to file
 - disambiguated countrynames/codes
 - wrote non-matched country-years to file
 - added deduplication asserts
erratum description file updated

 - problem less severe than thought initially!
small bugfixes
 - left countrynames in a few source datasets
 - CORES global variable left out of imp.R
misc changes for (hopefully) final hpc run