Log Message:
Update ruby-bundler pacakge to 1.0.21.

## 1.0.21 (September 30, 2011)

  - No changes from RC

## 1.0.21.rc (September 29, 2011)

Bugfixes:

  - Load Psych unless Syck is defined, because 1.9.2 defines YAML

## 1.0.20 (September 27, 2011)

Features:

  - Add platform :maglev (@timfel, #1444)

Bugfixes:

  - Ensure YAML is required even if Psych is found
  - Handle directory names that contain invalid regex characters

## 1.0.20.rc (September 18, 2011)

Features:

  - Rescue interrupts to `bundle` while loading bundler.rb (#1395)
  - Allow clearing without groups by passing `--without ''` (#1259)

Bugfixes:

  - Manually sort requirements in the lockfile (#1375)
  - Remove several warnings generated by ruby -w (@stephencelis)
  - Handle trailing slashes on names passed to `gem` (#1372)
  - Name modules for gems like 'test-foo_bar' correctly (#1303)
  - Don't require Psych if Syck is already loaded (#1239)

## 1.0.19.rc (September 13, 2011)

Features:

  - Compatability with Rubygems 1.8.10 installer changes
  - Report gem installation failures clearly (@rwilcox, #1380)
  - Useful error for cap and vlad on first deploy (@nexmat, @kirs)

Bugfixes:

  - `exec` now works when the command contains 'exec'
  - Only touch lock after changes on Windows (@robertwahler, #1358)
  - Keep load paths when #setup is called multiple times (@radsaq, #1379)