bool PrepareSaveAsFiles(SCHEMATIC &aSchematic, SCH_SCREENS &aScreens, const wxFileName &aOldRoot, const wxFileName &aNewRoot, bool aSaveCopy, bool aCopySubsheets, bool aIncludeExternSheets, std::unordered_map< SCH_SCREEN *, wxString > &aFilenameMap, wxString &aErrorMsg)