Obey program suffix when invoking bundler

If ruby is configured using --program-suffix or --program-prefix the
rake tasks will not be able to launch the correct bundler executable (as
"bundler" may not exist).

This uses Gem.default_exec_format to choose the correct "bundler" to
invoke in the rake task based on how Ruby was configured.
Ruby 2.0.0 support

Courtesy of @charliesome in #357
Correct version of Ruby for iconv
Fix spec
It works on my machine. Try tickling travis.
Merge pull request #324 from drbrain/obey_program_suffix

Obey program suffix when invoking bundler
Update History.md
Merge pull request #377 from cucumber/ruby-2.0.0

Ruby 2.0.0 support
Update History.md
Fall back on Test::Unit::Assertions if rspec-expectations is missing

Currently, users who don't want to use rspec-expectations have to do a
little extra setup in their env.rb to use Test::Unit.  Since Test::Unit
ships with Ruby (albeit as a wrapper in 1.9), it makes sense to look
for this library as a fallback.  This lowers the barrier even further
for users who want to jump straight into Cucumber with minimal
dependencies.
Add feature to check fallback to Test::Unit

The original implementation used require() to check for the presence of
RSpec.  This is difficult to test, because you'd have to stub out
require() at exactly the right time.

This commit reorganizes the code a bit to look for constants instead
(which are easy to override during testing).
Refactor
Update stepdefs.json
added after_step event, added code to before_step to capture time.now
added support for checking duration and to prevent test from breaking
adding a comment so travis will sync with my repo
Update RSpec
Fix tests for 1.8.7
Update stepdefs.json
Merge branch 'fcbeyer-jsonduration'

Capture duration value for json formatter. Closes #329