How IGB loads data from a DAS server.

This is the current procedure for loading data from DAS servers. Currently,
this only works on two DAS servers:

UCSC = http://genome.cse.ucsc.edu/cgi-bin/das/dsn
Ensembl = http://www.ensembl.org/das/dsn

Proposal for using the DAS registry to find data.

It is possible to use the DAS registry to find data on DAS servers,
the problem is that all DAS servers can be set up differently, they
all follow different rules or different DAS versions, some don't follow
all the protocol rules, and some are not maintained.
DAS is a protocol, and it has different versions. The spec for the
latest version (1.6) is at: http://www.biodas.org/documents/spec-1.6.html
the registry itself is at: http://www.dasregistry.org
So, for example, if we want to find servers for H_sapiens_Feb_2009,
we can use the query: http://www.dasregistry.org/das/sources?organism=9606&capability=features&version=37
and parse the results.