FTP: Redirect error to higher layer.

* Changes behavior of download function in ftp_utils.py. It was
  silencing the download error, now it is redirected to a higher
  layer.

Contrast_out: Change printed messages.
Merge branch 'master' of github.com:inspirehep/harvesting-kit

Conflicts:
	harvestingkit/ftp_utils.py
Merge pull request #58 from Dziolas/master

FTP: Redirect error to higher layer.