britney: Permit comments in Package-List field of constraints

python-apt's "TagFile" seems to cut the field short if it meets a
comment.  Therefore allow comments in the actual field value to avoid
this nasty behaviour.

Signed-off-by: Niels Thykier <niels@thykier.net>

britney.py

@@ -603,7 +603,7 @@ class Britney(object):
 
             self.log(" - constraint %s" % pkg_name, type='I')
 
-            pkg_list = [x.strip() for x in mandatory_field('Package-List').split("\n") if x.strip() != '']
+            pkg_list = [x.strip() for x in mandatory_field('Package-List').split("\n") if x.strip() != '' and not x.strip().startswith("#")]
             src_data = [faux_version,
                         faux_section,
                         [],