Add nginx configure hook

This adds a pluginhook for nginx-configure to be called after the main nginx configuration is called and before nginx is reloaded. This will allow other plugins to modify the nginx configuration
Merge pull request #189 from jeffutter/patch-1

Add nginx configure hook
Set X-Forwarded-Proto Header

Heroku passes the X-Forwarded-Proto header to indicate the protocol of
the incoming request[1]. Ruby's rack relies on this header to
determine if a request is HTTPS[2].

Also, the X-Scheme header was removed to eliminate redundant passing of
the scheme.

[1]: https://devcenter.heroku.com/articles/http-routing#heroku-headers
[2]: https://github.com/rack/rack/blob/master/lib/rack/request.rb#L77
Add X-Forwarded-Port and X-Request-Start

Adding additional proxy headers to match what Heroku provides. Also,
X-Request-Start is compatible with NewRelic's latest agent[1].

[1]: http://blog.newrelic.com/2013/02/21/using-new-relic-on-heroku-read-how-our-new-ruby-agent-measures-queue-time/
Merge pull request #204 from statianzo/forwarded-proto

Set X-Forwarded-Proto Header
Handle pipe failures
Use pre-built buildstep image from s3. Add option to build your own.
Merge pull request #215 from kanterov/master

Handle pipe failures
bootstrap.sh: Add shebang, Error out when apt-get is not found

...to fail more gracefully on systems without apt.
Support non-standard bash locations
resolves #236, adding support for dokku run commands to be interactive
added myself to authors
Merge pull request #237 from rajivm/make-run-interactive-236

resolves #236, adding support for dokku run commands to be interactive
Merge pull request #220 from jaseg/patch-2

bootstrap.sh: Add shebang, Error out when apt-get is not found
Merge pull request #221 from jaseg/patch-3

receiver: fix shebang for non-standard bash locations
Update Makefile: Do not try to install on "make" or "make all"

To be consistent with usual makefile usage and to not surprise people too much, only do permanent changes to the system when explicitely prompted to do so via "make install" instead of on any "make" or "make all" invocation, which is usually used for *building*, not *installing* things.
Added myself to AUTHORS - jaseg
normalise 'build' function args to match 'release' and 'deploy'
Merge pull request #219 from jaseg/patch-1

Update Makefile: Do not try to install on "make" or "make all"
Merge pull request #240 from jaseg/authors

Added myself to AUTHORS - jaseg