Merge branch 'ei/worktree+filter'

* ei/worktree+filter:
  filter-branch: always export GIT_DIR if it is set
  setup_git_directory: fix segfault if repository is found in cwd
  test GIT_WORK_TREE
  extend rev-parse test for --is-inside-work-tree
  Use new semantics of is_bare/inside_git_dir/inside_work_tree
  introduce GIT_WORK_TREE to specify the work tree
  test git rev-parse
  rev-parse: introduce --is-bare-repository
  rev-parse: document --is-inside-git-dir

connect.c

@@ -587,6 +587,7 @@ pid_t git_connect(int fd[2], char *url, const char *prog, int flags)
 			unsetenv(ALTERNATE_DB_ENVIRONMENT);
 			unsetenv(DB_ENVIRONMENT);
 			unsetenv(GIT_DIR_ENVIRONMENT);
+			unsetenv(GIT_WORK_TREE_ENVIRONMENT);
 			unsetenv(GRAFT_ENVIRONMENT);
 			unsetenv(INDEX_ENVIRONMENT);
 			execlp("sh", "sh", "-c", command, NULL);