angstrom-mirrors.bbclass adds angstrom-distribution.org as a BitBake
PREMIRROR for cvs, svn, git, hg, and bzr URIs, and a MIRROR for ftp,
http, and https URIs.
BitBake will try all PREMIRRORS for a given URI type first, then the
SRC_URI specified in the recipe, then all MIRRORS.
While in this case (http URI) trying angstrom-distribution.org means
that the original SRC_URI failed, it's worth pointing out that cvs,
svn, etc.. URIs do get hijacked by angstrom-distribution.org, which is
probably what you want in most cases, but that site has been slow as a
dog every time I've tried it. You are probably slightly more likely
to get a "known-good" version of the source from the PREMIRROR, but
often I'm willing to take my chances if it will save me several hours
of 5kbps downloads. I disable these premirrors in a duplicate
angstrom-mirrors.bbclass in a local overlay.