Fix undefined method .path on nil

Hi,

I got a undefined method call on .nil at line 106 of spring/application.rb.
After deeper investigation I've found out that my Gemfile didn't have sinatra, but other gem required it.
That caused spring to fail loading of rails app and crash.

This simple change checks that Rails.application is there before accessing it.

With this change it raises proper message that required file is not there.
replace and by &&
Merge pull request #246 from mikz/patch-1

Fix undefined method .path on nil
Test helper fix
Recommend 1.1 upgraders to regenerate binstubs
Add contributing guide [ci skip]

Closes #251.
Fix setting of process title causing rspec breakage

Fixes https://github.com/jonleighton/spring-commands-rspec/issues/7
Connect a PTY when preloading in background

Readline + libedit gets messed up if it loads when not connected to a
terminal. This resolves that problem.

Fixes #244.
Bump to version 1.1.1
Fix ActiveRecord connect/disconect
Added spinach command runner
Merge pull request #263 from jvanbaarsen/patch-1

Added spinach command runner
Fix CI

The method of activating the desired rails version was not working
correctly.
Test against Rails 4.1.0.rc1
Fix rails version selection

Previous code wasn't working correctly
Fix tests for rails 4.1
Abort when bin/spring is called and Spring is already defined

See #252. If you have a Spring 1.0 binstub, but Spring 1.1 on your
system, then the Spring 1.0 binstub will activate Spring 1.1, which will
then try to load your bin/rails, which will then load spring... and on
in on in a loop until you run out of memory. This prevents that and
prompts you to upgrade your binstubs.
Exit explicitly when running un-spring rails commands

Prevents "warning: already initialized constant APP_PATH" and
potentially other code from running that you don't expect to run.

Fixes #259.
Don't cache classes unless the environment permits it

Fixes #264.
Merge pull request #257 from fred/hotfix/256-active-record-fix

Fix ActiveRecord connect/disconect