repo/commit: Support group-writable files for bare-user-only

These exist in the wild for flatpak, and aren't really a problem. The canonical
permissions are still either `0755` or `0644`, we just support the additional
writable bit for the group (i.e. extend the set to include `0775` and `0664`)
now to avoid breaking some flatpak content.

Closes: #913
Approved by: alexlarsson

src/libostree/ostree-repo-commit.c

@@ -301,10 +301,10 @@ commit_loose_object_trusted (OstreeRepo        *self,
                self->mode == OSTREE_REPO_MODE_BARE_USER_ONLY
                && !object_is_symlink)
         {
-          guint32 invalid_modebits = (mode & ~S_IFMT) & ~0755;
+          guint32 invalid_modebits = (mode & ~S_IFMT) & ~0775;
           if (invalid_modebits > 0)
             return glnx_throw (error, "Invalid mode 0%04o with bits 0%04o in bare-user-only repository",
-                                   mode, invalid_modebits);
+                               mode, invalid_modebits);
 
           if (fchmod (fd, mode) < 0)
             return glnx_throw_errno_prefix (error, "fchmod");