Add ability to duplicate connections.
Mention :url option in README

Closes #391.
Run GC from test setup

I have seen a test run where the "connected_clients" field in the INFO output
changed from 15 to 3 over a statement where GC might run. This change should
prevent that from happening again.
Merge pull request #396 from redis/dup2

Add ability to duplicate connections.
Add Redis#dup to CHANGELOG
Fix off by 2 error in EXEC reply handling

The EXEC reply should have the same number of replies as there are commands in
the MULTI. This line of code expected the MULTI and EXEC commands themselves to
be part of the futures array, but they are not.

Note that this only surfaces for Redis versions < 2.6.5, because that is when
the EXECABORT error reply was introduced. Also see: antirez/redis@41f0f92.
Merge branch 'master' into ipv6

Conflicts:
	test/internals_test.rb