Tag compatibility. Resolves #1487 (#1492)

* Add --global-tag-lookup

* Add bin/gollum-migrate-tags

* Add migration tests (not on Travis)

test/test_migrate.rb

@@ -0,0 +1,52 @@
+# ~*~ encoding: utf-8 ~*~
+require File.expand_path(File.join(File.dirname(__FILE__), 'helper'))
+
+# Original contents of Subdir/Foo.md:
+# waa
+# [[Samwi]]
+# [[samwise gamgee.mediaWiki]]
+# [[Samwise Gamgee.mediawiki]]
+# [[Samwise Gamgee]]
+# [[Test|Samwise Gamgee#Anchor]]
+# [[Waaa|Test]]
+# [[Zaa]]
+
+# Contents of Subdir/Foo.md after successful tag migration
+result = <<EOF
+waa
+[[Samwi]]
+[[/Samwise Gamgee.mediawiki]]
+[[/Samwise Gamgee.mediawiki]]
+[[/Samwise Gamgee.md]]
+[[Test|/Samwise Gamgee.md#Anchor]]
+[[Waaa|/Bar/Test.md]]
+[[Subsub/Zaa.md]]
+EOF
+
+unless ENV['TRAVIS']
+
+  context '4.x -> 5.x tag migrator' do
+    include Rack::Test::Methods
+
+    setup do
+      @path = cloned_testpath("examples/lotr_migration.git")
+    end
+    
+    test 'repair broken links' do
+      PREFER_RELATIVE = true
+      RUN_SILENT = true
+      NO_DRY_RUN = true
+      script_path = File.expand_path(File.join(File.dirname(__FILE__), '../', 'bin', 'gollum-migrate-tags'))
+      Dir.chdir(@path) do
+        load script_path
+      end
+      f = File.new(::File.join(@path, 'Subdir/Foo.md'), 'r')
+      assert_equal result, f.read
+    end
+
+    teardown do
+      FileUtils.rm_rf(@path)
+    end
+  end
+
+end