Ability to pass additional arguments to localtime and getlocal.

http://www.ruby-doc.org/core-2.1.3/Time.html#method-i-getlocal accepts additional arguments to get Time object in particular time zone you want like this:
Time.now.getlocal(14400) # => 2014-10-13 16:21:02 +0400
This commit allows this for ActiveSupport::TimeWithZone objects so from now on you can do this:
Time.current.localtime         # => 2014-10-13 12:20:20 +0000
Time.current.getlocal          # => 2014-10-13 12:20:57 +0000
Time.current.localtime(14400)  # => 2014-10-13 16:22:04 +0400
Time.current.getlocal(-14400)  # => 2014-10-13 08:24:59 -0400
Time.zone.now.localtime        # => 2014-10-13 12:39:57 +0000
Time.zone.now.getlocal         # => 2014-10-13 12:40:01 +0000
Time.zone.now.localtime(-14400)# => 2014-10-13 08:40:55 -0400
Time.zone.now.getlocal(14400)  # => 2014-10-13 16:41:06 +0400