dependent_xref table added

sql/patch_54_55_d.sql

+# patch_54_55_d.sql
+#
+# title: Add table to store the dependent xrefs
+#
+# description:
+# For a given object_xref store its master if it is dependent on another xref (master)
+
+CREATE TABLE dependent_xref(
+     object_xref_id         INT NOT NULL,
+     master_xref_id         INT NOT NULL,
+     dependent_xref_id      INT NOT NULL,
+
+     PRIMARY KEY( object_xref_id ),
+     KEY dependent ( dependent_xref_id ),
+     KEY master_idx (master_xref_id)
+
+) COLLATE=latin1_swedish_ci TYPE=MyISAM;
+
+# patch identifier
+INSERT INTO meta (species_id, meta_key, meta_value) VALUES (NULL, 'patch', 'patch_54_55_d.sql|add_dependent_xref_table');
+