Updated Rack::Throttle::Limiter#http_error to return HTTP body as an array

On Ruby 1.9.3 and Rails 3.2.x, the server was returning empty response, due to:

    !! Unexpected error while processing request: undefined method `each' for "403 Forbidden (Rate Limit Exceeded)\n":String
Removed unused var.
Check whether HTTP_X_REQUEST_START or HTTP_X_QUEUE_START exist then parse its value (for example, when having New Relic in your stack, it's going to be in the "t=\d+" format)
Merge branch 'patch-1'
Fixed copy.
Merge branch 'master' of https://github.com/bendiken/rack-throttle

# By Winfield Peterson (6) and others
# Via Arto Bendiken (2) and others
* 'master' of https://github.com/bendiken/rack-throttle:
  fix README.md
  Add an optional callback to the Limiter base strategy.  This callback is fired whenever a rate limit is exceeded, to allow something like logging or per-app handling of rate limits.
  Update README for new Minute strategy.
  Properly scope app() method within describe block, fixes horrible race condition where this is over-ridden by each test you load, causing all kinds of weird failures if you run all specs as a group.
  Add throttling per-minute derived from Hourly throttling.
  Add Timecop based time tests.
  Convert to Bundler for dependency management.
  return an array of strings for 1.9

Conflicts:
	lib/rack/throttle/limiter.rb
Merge pull request #9 from lbeder/master

Fixed request start time detection when nginx is involved.