Ticket #11291: patch from "anon":

test-11291-group-redable-hsdirs-wtests-may8.patch
Clean up patch

Here I clean up anon's patch with a few of nickm's suggestions from comment 12:
https://trac.torproject.org/projects/tor/ticket/11291#comment:12

I did not yet completely implement all his suggestions.
Correct check_private_dir's dir mode

This commit attempts to satisfy nickm's comment on check_private_dir() permissions:
https://trac.torproject.org/projects/tor/ticket/11291#comment:12
"""check_private_dir() ensures that the directory has bits 0700 if CPD_CHECK_MODE_ONLY is not set. Shouldn't it also ensure that the directory has bits 0050 if CPD_CHECK_MODE_ONLY is not set, and CPD_GROUP_READ is set?"""
fix two typos
Make HiddenServiceDirGroupReadable per-hidden-service
Fix white space
Add Window compatibility note to docs

HiddenServiceDirGroupReadable has no effect in Windows
Fix regression nickm pointed out
Remove HiddenServiceDirGroupReadable from or_options_t

...and also fix whitespace.
Fix permissions logic
Additional test for error-case

This error-case was already fixed by previous changes,
this is to cover it in case there's a regression.
Merge remote-tracking branch 'meejah/ticket-11291-extra-utests'

Conflicts:
	src/or/config.c
11291: Fix warnings, add changes file, rename 'mask'.
chgrp the testing tempdir to ourself to clear the sticky bit

Closes 13678.  Doesn't actually matter for older tors.