envutil.rb: rename member

* test/ruby/envutil.rb (Test::Unit::Assertions::AssertFile): rename
  member to get rid of conflict with a method of Assertions.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39497 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* test/ruby/test_fnmatch.rb: use assert_file.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@39498 b2dd03c8-39d4-4d8f-98ff-823fe69b080e