Disease ontology improvements #101

Job	Run time
Tests (mysql, rails test test/unit)	20m 35s
Tests (mysql, rails test test/functional)	29m 31s
Tests (mysql, rails test test/integration)	14m 15s
Tests (mysql, rspec spec)	2m 41s
Tests (mysql, rake assets:precompile)	3m 6s
Tests (mysql, rake db:setup)	3m 6s
Tests (mysql, rake db:migrate)	2m 39s
Tests (mysql, rake seek:upgrade)	2m 56s
Tests (postgres, rails test test/unit)	20m 21s
Tests (sqlite3, rails test test/unit)	18m 46s
	1h 57m 56s

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