handle all knowns formats in Date#marshal_load

* fixes #878

lib/ruby/1.9/date.rb

@@ -1552,10 +1552,37 @@ def marshal_dump() [ajd, @of, @sg] end
 
   # Load from Marshal format.
   def marshal_load(a)
-    ajd, of, sg, = a
+    ajd, of, sg = nil
+
+    case a.size
+    when 2 # 1.6.x
+      ajd = a[0] - HALF_DAYS_IN_DAY
+      of = 0
+      sg = a[1]
+      sg = sg ? GREGORIAN : JULIAN unless Numeric === sg
+    when 3 # 1.8.x, 1.9.2
+      ajd, of, sg = a
+    when 6
+      _, jd, df, sf, of, sg = a
+      of = Rational(of, 86_400)
+      ajd = jd - HALF_DAYS_IN_DAY
+      ajd += Rational(df, 86_400) if df != 0
+      ajd += Rational(sf, 86_400_000_000_000) if sf != 0
+    else
+      raise TypeError, "invalid size"
+    end
+
     initialize(ajd, of, sg)
   end
 
+  def self._load(str)
+    ary = Marshal.load(str)
+    raise TypeError, "expected an array" unless Array === ary
+    obj = allocate
+    obj.marshal_load(ary)
+    obj
+  end
+
 end
 
 # Class representing a date and time.