Make sure explicit interface implementations can be parsed

Author: Per Gårdebrink

Diff for: tests/CommandLine.Tests/Fakes/Options_With_Only_Explicit_Interface.cs

@@ -0,0 +1,9 @@
+namespace CommandLine.Tests.Fakes
+{
+    class Options_With_Only_Explicit_Interface : IInterface_With_Two_Scalar_Options
+    {
+        bool IInterface_With_Two_Scalar_Options.Verbose { get; set; }
+
+        string IInterface_With_Two_Scalar_Options.InputFile { get; set; }
+    }
+}

Diff for: tests/CommandLine.Tests/Unit/Core/InstanceBuilderTests.cs

@@ -789,6 +789,20 @@ public void Specifying_options_two_or_more_times_with_mixed_short_long_options_g
             ((NotParsed<Simple_Options>)result).Errors.Should().HaveCount(x => x == expected);
         }
 
+        [Theory]
+        [InlineData(new[] { "--inputfile=file1.bin" }, "file1.bin")]
+        [InlineData(new[] { "--inputfile", "file2.txt" }, "file2.txt")]
+        public void Can_define_options_on_explicit_interface_properties(string[] arguments, string expected) 
+            {
+            // Exercize system
+            var result = InvokeBuild<Options_With_Only_Explicit_Interface>(
+                arguments);
+
+            // Verify outcome
+            expected.Should().BeEquivalentTo(((IInterface_With_Two_Scalar_Options)((Parsed<Options_With_Only_Explicit_Interface>)result).Value).InputFile);
+        }
+
+
         [Theory]
         [InlineData(new[] { "--inputfile=file1.bin" }, "file1.bin")]
         [InlineData(new[] { "--inputfile", "file2.txt" }, "file2.txt")]