Python3 migration: updated evaluation of source files
date::checkfinite function now defined in the header. No longer external function call
+ ability to link to frepple as static library (useful in only very few, specific cases)
Deletesolver now exporting some extra symbols on windows.
+ public method to get commandlist of a solver
Extra method to write the header of an XML file.
(Currently not in Community Edition, but not really important anyway to keep close)