Extract simple platform checks from Rakefile, gemspec, spec_helper

As a first step to updating dependencies while maintaining compatibility,
extract common simple platform detection helpers.

Rakefile

@@ -1,6 +1,7 @@
 require 'rake/clean'
 require 'bundler/gem_tasks'
 require 'rspec/core/rake_task'
+require File.expand_path('on_what', File.dirname(__FILE__))
 
 # Default task for `rake` is to run rspec
 task :default => [:spec]
@@ -11,12 +12,13 @@ RSpec::Core::RakeTask.new
 # Configure `rake clobber` to delete all generated files
 CLOBBER.include('pkg', 'doc', 'coverage')
 
-# Only configure yard doc generation when *not* on Travis
-if ENV['CI'] != 'true'
-  require "github/markup"
-  require "redcarpet"
-  require "yard"
-  require "yard/rake/yardoc_task"
+# To limit needed compatibility with versions of dependencies, only configure
+#   yard doc generation when *not* on Travis, JRuby, or 1.8
+if !on_travis? && !on_jruby? && !on_1_8?
+  require 'github/markup'
+  require 'redcarpet'
+  require 'yard'
+  require 'yard/rake/yardoc_task'
 
   YARD::Rake::YardocTask.new do |t|
     OTHER_PATHS = %w()

docile.gemspec

@@ -1,3 +1,4 @@
+require File.expand_path('on_what', File.dirname(__FILE__))
 $:.push File.expand_path('../lib', __FILE__)
 require 'docile/version'
 
@@ -23,7 +24,9 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rspec', '~> 2.14.0'
   s.add_development_dependency 'mime-types', '~> 1.25.1'
 
-  if !(defined?(RUBY_ENGINE) && 'jruby' == RUBY_ENGINE)
+  # To limit needed compatibility with versions of dependencies, only configure
+  #   yard doc generation when *not* on Travis, JRuby, or 1.8
+  if !on_travis? && !on_jruby? && !on_1_8?
     # Github flavored markdown in YARD documentation
     # http://blog.nikosd.com/2011/11/github-flavored-markdown-in-yard.html
     s.add_development_dependency 'yard'

on_what.rb

@@ -0,0 +1,14 @@
+# NOTE: Very simple tests for what system we are on, extracted for sharing
+#   between Rakefile, gemspec, and spec_helper. Not for use in actual library.
+
+def on_travis?
+  ENV['CI'] == 'true'
+end
+
+def on_jruby?
+  (defined?(RUBY_ENGINE) && 'jruby' == RUBY_ENGINE)
+end
+
+def on_1_8?
+  RUBY_VERSION.start_with? '1.8'
+end

spec/spec_helper.rb

@@ -1,9 +1,11 @@
+require File.expand_path('on_what', File.dirname(File.dirname(__FILE__)))
+
 begin
   require 'simplecov'
   require 'coveralls'
 
   # On Ruby 1.9+ use SimpleCov and publish to Coveralls.io
-  if !RUBY_VERSION.start_with? '1.8'
+  if !on_1_8?
     SimpleCov.formatter = SimpleCov::Formatter::MultiFormatter[
       SimpleCov::Formatter::HTMLFormatter,
       Coveralls::SimpleCov::Formatter