Increase curl timeout to two minutes

In #165, a few users are getting time outs.

```
  Compiling Ruby
 !
    ERROR: Command: 'set -o pipefail; curl --fail --retry 3 --retry-delay 1 --connect-timeout 3 --max-time 20 https://s3-external-1.amazonaws.com/heroku-buildpack-ruby/ruby-1.9.3-jruby-1.7.3.tgz -s -o - | tar zxf -' failed unexpectedly:
    ERROR: 
    ERROR: gzip: stdin: invalid compressed data--format violated
    ERROR: tar: Unexpected EOF in archive
    ERROR: tar: Unexpected EOF in archive
    ERROR: tar: Error is not recoverable: exiting now
 !
```
make curl max_timeout variable with env.
[ci skip] Changelog
[fix #182] Show Warning In-line for Windows Gems

When deploying a Gemfile.lock that has been generated via windows, we must remove the file which can cause bundler to not be able to resolve.

When bundler does not resolve, the end user never sees the windows warning message due to the resolver never finishing (since warnings are saved until the end of the output).

This change allows warnings to be emitted inline and changes the default behavior of the windows warning to display before the `bundle install` is run, thus mitigating this problem.

Even when the `bundle install` fails the warnings are not displayed since the process `exits` rather than continues to print out the warnings.

Here is a link to the devcenter article I wrote for this PR https://devcenter.heroku.com/articles/bundler-windows-gemfile
Fix year in changelog
Merge pull request #187 from dgrizzanti/patch-1

Fix year in changelog
Merge pull request #182 from heroku/schneems/better-windows-warning

[fix #182] Show Warning In-line for Windows Gems
If a manifest file was detected skip rake detect

When a user is deploying with a manifest, we don't not need to load up their Rake to see if they have the `asset:precompile` task. Changing the order of the checks prevents users from seeing debugging information that is not needed and helps speed up apps by doing less work.
Merge pull request #188 from heroku/schneems/no-rake-if-manifest

If a manifest file was detected skip rake detect
[ci skip] changelog
don't require rake to be present for Ruby 1.9+
Merge pull request #175 from icco/patch-1

Allow curl timeout to be configurable
ruby 1.9 also has rake in stdlib
add rake detect tests
un-focus test
Merge pull request #190 from heroku/schneems/rake-version

don't require rake to be present for Ruby 1.9+
Hide default bundler clean output
Fix LPXC deadlock issue 

ryandotsmith/lpxc#7
Merge pull request #174 from heroku/schneems/less-verbose-default-cache

Hide default bundler clean output
remove rake tasks that use vulcan

the buildpack uses [hammer](http://github.com/hone/hammer)