Add a standard --url argument to all scripts.

redis-py now supports URL-based connection configuration.  When --url
is specified, we use it to construct the Redis object.  Otherwise, we
use the existing argument-based construction method.

`Redis.from_url()` is new in redis-py 2.6.2, so that prerequisite has
been adjusted accordingly.

rq/scripts/__init__.py

@@ -5,6 +5,8 @@ from rq import use_connection
 def add_standard_arguments(parser):
     parser.add_argument('--config', '-c', default=None,
             help='Module containing RQ settings.')
+    parser.add_argument('--url', '-u', default=None,
+            help='URL describing Redis connection details')
     parser.add_argument('--host', '-H', default=None,
             help='The Redis hostname (default: localhost)')
     parser.add_argument('--port', '-p', default=None,
@@ -44,6 +46,9 @@ def setup_default_arguments(args, settings):
 
 
 def setup_redis(args):
+    if args.url is not None:
+        redis_conn = redis.Redis.from_url(args.url, db=args.db)
+    else:
         redis_conn = redis.Redis(host=args.host, port=args.port, db=args.db,
             password=args.password)
     use_connection(redis_conn)

setup.py

@@ -17,7 +17,7 @@ def get_version():
 
 
 def get_dependencies():
-    deps = ['redis >= 2.4.0', 'times']
+    deps = ['redis >= 2.6.2', 'times']
     deps += ['logbook']  # should be soft dependency?
     if sys.version_info < (2, 7) or \
             (sys.version_info >= (3, 0) and sys.version_info < (3, 1)):