Improve Gallica public domain detection

[nemobis]

Vigneron reports that http://gallica.bnf.fr/ark:/12148/bpt6k933829z/ isn't identified as being in the public domain. I think

BUB/digi-lib/gal.py

Lines 102 to 107 in e7e0010

	for i in strong_attr:
	public_domain = get_metadata(i, specific_tag = 'Droits')
	if not public_domain:
	continue
	if 'domaine public' in public_domain.encode('utf-8'):
	return 0

is needlessly complicated; now in the HTML I see <meta name="DC.rights" content="domaine public" /> <meta name="DC.rights" content="public domain" />, BUB can just parse that.

[rohit-dua]

patch: f0f3740