Merge branch 'nd/stop-setenv-work-tree'

An earlier change in 2.5.x-era broke users' hooks and aliases by
exporting GIT_WORK_TREE to point at the root of the working tree,
interfering when they tried to use a different working tree without
setting GIT_WORK_TREE environment themselves.

* nd/stop-setenv-work-tree:
  Revert "setup: set env $GIT_WORK_TREE when work tree is set, like $GIT_DIR"

t/t0002-gitfile.sh

@@ -99,7 +99,7 @@ test_expect_success 'check rev-list' '
 	test "$SHA" = "$(git rev-list HEAD)"
 '
 
-test_expect_success 'setup_git_dir twice in subdir' '
+test_expect_failure 'setup_git_dir twice in subdir' '
 	git init sgd &&
 	(
 		cd sgd &&