[ruby/date] Fix comparison with Float::INFINITY

Fixes [Bug #17945]

https://github.com/ruby/date/commit/953d907238

ext/date/lib/date.rb

@@ -30,6 +30,8 @@ class Date
     def <=>(other)
       case other
       when Infinity; return d <=> other.d
+      when Float::INFINITY; return d <=> 1
+      when -Float::INFINITY; return d <=> -1
       when Numeric; return d
       else
         begin

test/date/test_date.rb

@@ -163,4 +163,16 @@ class TestDate < Test::Unit::TestCase
     assert_equal(1, d2 <=> d1)
   end
 
+  def test_infinity_comparison
+    assert_equal(0, Float::INFINITY <=> Date::Infinity.new)
+    assert_equal(0, Date::Infinity.new <=> Float::INFINITY)
+    assert_equal(0, -Float::INFINITY <=> -Date::Infinity.new)
+    assert_equal(0, -Date::Infinity.new <=> -Float::INFINITY)
+
+    assert_equal(1, Float::INFINITY <=> -Date::Infinity.new)
+    assert_equal(1, Date::Infinity.new <=> -Float::INFINITY)
+
+    assert_equal(-1, -Float::INFINITY <=> Date::Infinity.new)
+    assert_equal(-1, -Date::Infinity.new <=> Float::INFINITY)
+  end
 end