don't warn about sudo on windows

fixes #2984
Implemented a very basic plugin system.

The way this works is pretty much the same way as `git` commands work.

When invoking `bundler <task>`, if the task isn't defined on Bundler::CLI,
Bundler will try and figure out if there is a `bundler-<task>` binary
present on the path. If so, it's invoked.

Same error message (and error codes) apply when a binary isn't found.

Also, this is just a first, simple pass at the problem. @indirect and I
had a chat about how it should work, and we should probably think about
offering the possibility of loading up Ruby plugins in the already
loaded Bundler environment.
Add failing spec for #3004.
Switch to thread workers from unix workers for MRI
Fix use of deprecated failure_message_should

- Replaced with failure_message
Merge pull request #3043 from prathamesh-sonpatki/fix-deprecation-warning-for-failure-message-should

Fix use of deprecated failure_message_should

[ci skip]
Extract standalone path expansion to do it only once
Merge pull request #3044 from Juanxo/extract-standalone-path-expansion

Extract standalone path expansion to do it only once
fix the rspec rake task on 1.8.7
check rspec version while running specs
add travis results to slack #general room

[ci skip]
Update Travis config w/correct rbx version
Merge pull request #3047 from jc00ke/master

Update Travis config w/correct rbx version
Don't include configured source credentials in lockfile.
Add `bundle viz --without` to exclude gem groups from resulting graph.

This commit introduces a `--without` flag (similar to the flag on the
`install` subcommand) which will drop the inclusion of these gems from
the graph.

The ability to exclude gem groups from the graph is very useful when
trying to visualize or understand the runtime dependencies of a
particular RubyGem or project, minus any development or test related
libraries.

Previously the process of reproducing this behavior was a manual
process:

* Inspect the project's Gemfile and comment/remove any gems that are not
  runtime dependencies. Typically these gems would be in `:test` or
  `:development` groups.
* Inspect the project's gemspec (if it exists) and comment/remove any
  gems that are not runtime dependencies.

Now it is as simple as:

    bundle viz --without=test development
Simplified suppress_configured_credentials and made it run on Ruby 1.8.
Merge pull request #3049 from lhz/fix-configured-credentials-in-lock

Don't store configured source credentials in Gemfile.lock

Conflicts:
	CHANGELOG.md
Merge pull request #3050 from fnichol/viz-without-groups

Add `bundle viz --without` to exclude gem groups from resulting graph.
Fix travis Slack notification
Merge pull request #3052 from arthurnn/patch-1

Fix travis Slack notification