Make HashWithIndifferentAccess handle reverse_merge

Fixes #543

lib/thor/core_ext/hash_with_indifferent_access.rb

@@ -51,6 +51,18 @@ def merge!(other)
         self
       end
 
+      def reverse_merge(other)
+        self.class.new(other).merge(self)
+      end
+
+      def reverse_merge!(other_hash)
+        replace(reverse_merge(other_hash))
+      end
+
+      def replace(other_hash)
+        super(other_hash)
+      end
+
       # Convert to a Hash with String keys.
       def to_hash
         Hash.new(default).merge!(self)

spec/core_ext/hash_with_indifferent_access_spec.rb

@@ -60,4 +60,22 @@
     expect(@hash.to_hash.class).to eq(Hash)
     expect(@hash).to eq("foo" => "bar", "baz" => "bee", "force" => true)
   end
+
+  it "handles reverse_merge" do
+    other = {:foo => "qux", "boo" => "bae"}
+    new_hash = @hash.reverse_merge(other)
+
+    expect(@hash.object_id).not_to eq(new_hash.object_id)
+    expect(new_hash[:foo]).to eq("bar")
+    expect(new_hash[:boo]).to eq("bae")
+  end
+
+  it "handles reverse_merge!" do
+    other = {:foo => "qux", "boo" => "bae"}
+    new_hash = @hash.reverse_merge!(other)
+
+    expect(@hash.object_id).to eq(new_hash.object_id)
+    expect(new_hash[:foo]).to eq("bar")
+    expect(new_hash[:boo]).to eq("bae")
+  end
 end