Make several small string fixes in linearize-data.py

- Add a space after the fixed string prepended to file names when input or
  output file changes
- Clarify the error message when the genesis block is not found in the
  hash list (...why do we have this at all?)

contrib/linearize/linearize-data.py

@@ -292,7 +292,7 @@ if __name__ == '__main__':
 	blkmap = mkblockmap(blkindex)
 
 	if not "000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f" in blkmap:
-		print("not found")
+		print("Genesis block (000000000019d6689c085ae165831e934ff763ae46a2a6c172b3f1b60a8ce26f) not found in hashlist")
 	else:
 		BlockDataCopier(settings, blkindex, blkmap).run()