Revert "Do not always taint the result of File#path"

This reverts commit 1a759bfe5d.

This fails on some operating systems.

file.c

@@ -475,7 +475,7 @@ rb_file_path(VALUE obj)
         rb_raise(rb_eIOError, "File is unnamed (TMPFILE?)");
     }
 
-    return rb_str_dup(fptr->pathv);
+    return rb_obj_taint(rb_str_dup(fptr->pathv));
 }
 
 static size_t

test/readline/test_readline.rb

@@ -41,11 +41,6 @@ module BasetestReadline
       assert_equal("> ", stdout.read(2))
       assert_equal(1, Readline::HISTORY.length)
       assert_equal("hello", Readline::HISTORY[0])
-
-      # Work around lack of SecurityError in Reline
-      # test mode with tainted prompt
-      return if kind_of?(TestRelineAsReadline)
-
       Thread.start {
         $SAFE = 1
         assert_raise(SecurityError) do

test/ruby/test_file_exhaustive.rb

@@ -187,22 +187,6 @@ class TestFileExhaustive < Test::Unit::TestCase
     end
   end
 
-  def test_path_taint
-    [regular_file, utf8_file].each do |file|
-      assert_equal(false, File.open(file) {|f| f.path}.tainted?)
-      assert_equal(true, File.open(file.dup.taint) {|f| f.path}.tainted?)
-      o = Object.new
-      class << o; self; end.class_eval do
-        define_method(:to_path) { file }
-      end
-      assert_equal(false, File.open(o) {|f| f.path}.tainted?)
-      class << o; self; end.class_eval do
-        define_method(:to_path) { file.dup.taint }
-      end
-      assert_equal(true, File.open(o) {|f| f.path}.tainted?)
-    end
-  end
-
   def assert_integer(n)
     assert_kind_of(Integer, n)
   end