nokogiri should compile with system libs

As of nokogiri 1.6.0, they default to using the vendored libxml2 libs.
This is problematic for two reasons. First, with the way the heroku
build environment works,
https://github.com/sparklemotion/nokogiri/issues/923. This means it
won't link nokogiri.so properly since it's dependent on hardcoded paths
that don't exist during runtime. Second, compiling libxml2 and friends
is unnecessary since we have them already setup. We should skip this to
speed up deploys.
Merge pull request #124 from heroku/nokogiri

nokogiri should compile with system libs
update changelog
v77
dont install plugins if plugins exist as gems
Warning when plugin gets installed

avoids the 'topic' output entirely if no plugins need to be installed
use if.any?
Merge pull request #11 from heroku/skip-plugins-if-gems

Skip plugins if gems
add intelligent messaging for the nokogiri fix
Merge tag 'v77'
[close #127] Fix LPXC Deadlock Error

LPXC can experience a deadlock error reported in #127 it was fixed in this commit:
https://github.com/ryandotsmith/lpxc/commit/1f0bd9c31324cac109a94f70589f62652b0146a3

We are vendoring those changes in in this commit
Merge pull request #128 from heroku/schneems/lpxc-fix

[close #127] Fix LPXC Deadlock Error
Clean up plugin logic and warning text

added a test
Merge pull request #126 from heroku/schneems/plugin-warnings

Clean up plugin logic and warning text
Bugfix and More tests for plugin logic
Merge pull request #132 from heroku/schneems/less-inheritance-in-plugins

Bugfix and More tests for plugin logic
Revert "Merge pull request #132 from heroku/schneems/less-inheritance-in-plugins"

This reverts commit 968736e977fcb54705d2fe2a95f11f2192026d17, reversing
changes made to 34f5f706158d55fbeabc548c5fbd0f851e547fd6.

Still some issues with this Pull Request. Going to work on it some more.
remove extra '--' from warnings
Symlink ruby.exe to ruby

Rails 4 introduced the `bin/` directory to generated projects with executables `rails`, `bundle`, `rake`, etc. The file generated on windows has a link to an incorrect `ruby.exe` in the shebang line. See #134.

This PR adds a symlink so that `ruby.exe` can be called in addition to `ruby.
should set $GEM_PATH as well for the build process

if this isn't setup properly, locally it might pick the wrong bundler