Extend db_name in external_db table to 40 characters (from 28)

sql/patch_50_51_h.sql

+# patch_50_51_h.sql
+#
+# title: External_db name
+#
+# description:
+# Extend db_name in external_db table to 40 characters (from 28)
+
+ALTER TABLE external_db CHANGE COLUMN db_name db_name VARCHAR(40) NOT NULL;
+
+# patch identifier
+INSERT INTO meta (species_id, meta_key, meta_value) VALUES (NULL, 'patch', 'patch_50_51_h.sql|external_db_db_name');
+
+