lib/checkout: Add bareuseronly_dirs option

This is a continuation of https://github.com/ostreedev/ostree/pull/926
for directories instead of files.

See: https://github.com/flatpak/flatpak/issues/845

This option suppresses mode bits outside of `0775` for directory
checkouts.  I think most people should start doing this by default,
and use explicit overrides for e.g. `/tmp` if doing a recommit based
on a checkout.

Closes: #927
Approved by: alexlarsson

src/libostree/ostree-repo-checkout.c

@@ -751,11 +751,11 @@ checkout_tree_at_recurse (OstreeRepo                        *self,
     {
       guint32 canonical_mode;
       /* Silently ignore world-writable directories (plus sticky, suid bits,
-       * etc.) when doing a checkout for bare-user-only repos. This is related
-       * to the logic in ostree-repo-commit.c for files.
+       * etc.) when doing a checkout for bare-user-only repos, or if requested explicitly.
+       * This is related to the logic in ostree-repo-commit.c for files.
        * See also: https://github.com/ostreedev/ostree/pull/909 i.e. 0c4b3a2b6da950fd78e63f9afec602f6188f1ab0
        */
-      if (self->mode == OSTREE_REPO_MODE_BARE_USER_ONLY)
+      if (self->mode == OSTREE_REPO_MODE_BARE_USER_ONLY || options->bareuseronly_dirs)
         canonical_mode = (mode & 0775) | S_IFDIR;
       else
         canonical_mode = mode;

src/libostree/ostree-repo.h

@@ -768,7 +768,8 @@ typedef struct {
   gboolean process_whiteouts;
   gboolean no_copy_fallback;
   gboolean force_copy; /* Since: 2017.6 */
-  gboolean unused_bools[6];
+  gboolean bareuseronly_dirs; /* Since: 2017.7 */
+  gboolean unused_bools[5];
 
   const char *subpath;