Update capistrano to 2.13.3.

## 2.13.3 / August 21 2012

This release contains multiple bugfixes and handling of exotic situations. The
`Configuration#capture` method should now work in spite of `ActiveSupport`
shenanigans. Thank you, the community, for all of your contributions:

* Close input streams when sending commands that don't read input. Dylan Smith
  (dylanahsmith)
* Listen for method definition on `Kernel` and undefine on `Namespace`. Chris
  Griego (cgriego)
* Fixed shell `Thread.abort_on_exception` bug. George Malamidis (nutrun)
* Adding a log method to `Capistrano::Deploy::SCM::None` to maintain
  consistency with other SCM classes. Kevin Lawver (kplawver)
* Add deprecation warning if someone uses old `deploy:symlink` syntax on
  callbacks. Ken Mazaika (kenmazaika)
* Simplify the `finalize_update` code by respecting the `:shared_children`
  variable during removal and recreation of the parent. John Knight
  (knightlabs)

(taca)