Disease ontology improvements #102

Job	Run time
Tests (mysql, rails test test/unit)	21m 59s
Tests (mysql, rails test test/functional)	28m 30s
Tests (mysql, rails test test/integration)	14m 9s
Tests (mysql, rspec spec)	2m 39s
Tests (mysql, rake assets:precompile)	2m 59s
Tests (mysql, rake db:setup)	2m 41s
Tests (mysql, rake db:migrate)	2m 34s
Tests (mysql, rake seek:upgrade)	3m 17s
Tests (postgres, rails test test/unit)	19m 53s
Tests (sqlite3, rails test test/unit)	17m 19s
	1h 56m 0s

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