I only tested this with libical-0.44-r1, and I did not compare new checksums to existing ones. However, if there are no surprises, all three ebuilds should work with: SRC_URI="mirror://sourceforge/freeassociation/${PN}/${P}/${P}.tar.gz"
Still broken, Mr. Anderson's correction (remove '/files' from SRC_URI) seems to work...
Today's bump, libical-0.48.ebuild, is failing for the same reason. Correcting the SRC_URI fixes it.
+ 05 Jan 2012; Patrick Lauer <patrick@gentoo.org> libical-0.48.ebuild: + Fixing SRC_URI, see #350193