.acl lookup breaks when the path contains spaces

[RubenVerborgh]

When accessinghttps://foo.bar/abc/def%20ghi/ in presence of the following .acl files:

1. https://foo.bar/abc/def%20ghi/.acl
2. https://foo.bar/abc/.acl
   the first .acl file should be preferred over the second.

In practice, because of the spaces in the first, the second is chosen instead.

[RubenVerborgh]

Addressed by #660.