Improve performance some Numeric methods [Feature #17632] (#4190)

Merged-By: k0kubun <takashikkbn@gmail.com>

numeric.rb

@@ -1,3 +1,49 @@
+class Numeric
+  #
+  #  call-seq:
+  #     num.real?  ->  true or false
+  #
+  #  Returns +true+ if +num+ is a real number (i.e. not Complex).
+  # 
+  def real?
+    return true
+  end
+
+  #
+  #  call-seq:
+  #     num.integer?  ->  true or false
+  #
+  #  Returns +true+ if +num+ is an Integer.
+  #
+  #      1.0.integer?   #=> false
+  #      1.integer?     #=> true
+  # 
+  def integer?
+    return false
+  end
+
+  #
+  #  call-seq:
+  #     num.finite?  ->  true or false
+  #
+  #  Returns +true+ if +num+ is a finite number, otherwise returns +false+.
+  #
+  def finite?
+    return true
+  end
+
+  #
+  #  call-seq:
+  #     num.infinite?  ->  -1, 1, or nil
+  #
+  #  Returns +nil+, -1, or 1 depending on whether the value is
+  #  finite, <code>-Infinity</code>, or <code>+Infinity</code>.
+  #
+  def infinite?
+    return nil
+  end
+end
+
 class Integer
   # call-seq:
   #    -int  ->  integer