Add specs for the x64-mingw32 platform.
Add proper support for x64-mingw32 platform.

This fixes github issue #2356 .
Add more variants to specs for GemHelpers#generic
Remove useless code from GemHelpers#generic
Merge pull request #2584 from xaviershay/issue-2430

Less confusing message in 'use bundle exec' error message.
Merge pull request #2585 from xaviershay/bundler-features

Add references to new bundler features repo.
rearrange docs a bit to be less silly
oh yeah new domain
Merge pull request #2590 from larskanis/add_x64-mingw32_support

Add support for the x64-mingw32 platform
link to small bugs and features

[ci skip]
rubygems 2.0.6 and build against 2.0 stable branch
and with the task
Revert "Merge pull request #2569 from fuadsaud/github-https"

This reverts commit e2a5d3b90d8c1d685acc6d1a9d9cc3488b2c1a61, reversing
changes made to 435307266d75c82e7601f39551b0b707c58dc9a4.

fixes #2600
`bundler` bin for those who confuse it with `bundle`
Merge pull request #2598 from kirs/bundler-bin

`bundler` bin for those who confuse it with `bundle`
Don't allow to use bundler/capistrano with cap 3.x
Merge pull request #2597 from kirs/capistrano-3-warnings

Don't allow to use bundler/capistrano with cap 3.x
When git gem install fails, don't suggest `gem install foo`
Ignore git path configuration in env when shelling out to git.