Fix shared gems to be deduplicated

Gemfile

@@ -3,3 +3,4 @@ source 'https://rubygems.org'
 gemspec name: 'mutant'
 
 gem 'devtools', git: 'https://github.com/rom-rb/devtools.git'
+eval_gemfile File.expand_path('../Gemfile.shared', __FILE__)

Gemfile.shared

@@ -0,0 +1,3 @@
+# Place for shared git sources, used for developing updates to depedencies 
+# where the git sources (without this file) need to be consistently edited 
+# into multiple Gemfiles.

spec/support/corpus.rb

@@ -134,6 +134,7 @@ def install_mutant
         repo_path.join('Gemfile').open('a') do |file|
           file << "gem 'mutant', path: '#{relative}'\n"
           file << "gem 'mutant-rspec', path: '#{relative}'\n"
+          file << "eval_gemfile File.expand_path('#{relative.join('Gemfile.shared')}')\n"
         end
         lockfile = repo_path.join('Gemfile.lock')
         lockfile.delete if lockfile.exist?

test_app/Gemfile.rspec3.2

@@ -4,3 +4,4 @@ gem 'rspec-core', '~> 3.2.0'
 gem 'mutant',       path: '../'
 gem 'mutant-rspec', path: '../'
 gem 'adamantium'
+eval_gemfile File.expand_path('../../Gemfile.shared', __FILE__)

test_app/Gemfile.rspec3.3

@@ -4,3 +4,4 @@ gem 'rspec-core', '~> 3.3.0'
 gem 'mutant',       path: '../'
 gem 'mutant-rspec', path: '../'
 gem 'adamantium'
+eval_gemfile File.expand_path('../../Gemfile.shared', __FILE__)