* lib/fileutils.rb: use Object#is_a? instead of Class#=== to allow e.g. remote objects for receivers.
* lib/fileutils.rb: FileTest -> File.
* lib/fileutils.rb: put parentheses for arguments of File.xxxx?
* test/fileutils/test_fileutils.rb (test_cp): test "cp a a".
* test/fileutils/test_fileutils.rb (test_mv): test "mv a a".
* test/fileutils/test_fileutils.rb (test_ln): test "ln a a".
* test/fileutils/test_fileutils.rb (test_ln_s): test "ln_s a a".
* test/fileutils/test_fileutils.rb (test_install): test "install a a".
* test/fileutils/fileasserts.rb: new method assert_symlink.
* test/fileutils/fileasserts.rb: assert_is_directory -> assert_directory.
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4976 b2dd03c8-39d4-4d8f-98ff-823fe69b080e