libxml2-devel, from main distro.
mod_dav_acl, see web link above.
To compile mod_dav_acl requires a patch in Apache. The patch is included with the mod_dav_acl sources. Versions available on Build Service:
None of these have the patch. How motivated am I to test mod_caldav? Enough to get tangled up with a patched version of Apache? I don't think so.