add O_CLOEXEC (close-on-exec) flag to open(2) calls suggested by millert ok thomas_adam

portable: remove queue.h queue.h is included portably, so it shouldn't be included directly.

let gotadmin find the repository automatically if invoked in a work tree Move a small amount of code from worktree.c to a new file worktree_open.c, which contains everything required to open and close a work tree and inspect some of its basic parameters. This can be used by gotadmin. ok tracey