fix bing "garbage" results (issue #1275)

searx/engines/bing.py

 from lxml import html
 from searx.engines.xpath import extract_text
 from searx.url_utils import urlencode
-from searx.utils import match_language
+from searx.utils import match_language, gen_useragent
 
 # engine dependent config
 categories = ['general']
         offset=offset)
 
     params['url'] = base_url + search_path
+
+    params['headers']['User-Agent'] = gen_useragent('Windows NT 6.3; WOW64')
+
     return params
 
 

searx/utils.py

                 'style')
 
 
-def gen_useragent():
+def gen_useragent(os=None):
     # TODO
-    return ua.format(os=choice(ua_os), version=choice(ua_versions))
+    return ua.format(os=os or choice(ua_os), version=choice(ua_versions))
 
 
 def searx_useragent():