message: Fix recognition of uppercase file extensions
  Correctly recognize files dragged to Poedit's window that have uppercase
  extension (e.g. ."XLF"). This was handled correctly when opening files,
  but not in Catalog::CanLoadFile() used by the drag and drop target.
diff: @@ -1079,8 +1079,10 @@ CatalogPtr Catalog::Create(const wxString& filename, int flags)
  return cat;
  }
  -bool Catalog::CanLoadFile(const wxString& extension)
  +bool Catalog::CanLoadFile(const wxString& extension_)
  {
  + auto extension = extension_.Lower();
  +
  return POCatalog::CanLoadFile(extension) ||
  XLIFFCatalog::CanLoadFile(extension);
  }
  