Foreign key creation and index renaming in wrong order on MySQL < 5.7

[fust]

When using schema-tool:update or migrations:diff on a MySQL < 5.7 the renaming of indices and the creation of foreign keys is in the wrong order which causes index updates to fail.

For example, this is what would be expected:

ALTER TABLE form_results DROP FOREIGN KEY form_results_forms_id;
ALTER TABLE form_results CHANGE form_id form_id INT DEFAULT NULL, CHANGE element_name element_name VARCHAR(255) NOT NULL;
DROP INDEX form_id ON form_results;
CREATE INDEX IDX_603CFEA45FF69B7D ON form_results (form_id);
ALTER TABLE form_results ADD CONSTRAINT FK_603CFEA45FF69B7D FOREIGN KEY (form_id) REFERENCES forms (id);

And this is what is actually generated:

ALTER TABLE form_results DROP FOREIGN KEY form_results_forms_id;
ALTER TABLE form_results CHANGE form_id form_id INT DEFAULT NULL, CHANGE element_name element_name VARCHAR(255) NOT NULL;
ALTER TABLE form_results ADD CONSTRAINT FK_603CFEA45FF69B7D FOREIGN KEY (form_id) REFERENCES forms (id);
DROP INDEX form_id ON form_results;
CREATE INDEX IDX_603CFEA45FF69B7D ON form_results (form_id);

As a temporary solution i've changed the order in which AbstractPlatform generates the SQL so the foreign keys get added last (Move rows 2081 - 2089 after 2106) but I don't think that solves this issue without breaking other platforms.

[Ocramius]

@deeky666 wondering if we can move towards dropping some platforms, at this point.

[fust]

@Ocramius : I agree about dropping support for old versions, though I think MySQL 5.6 should be the minimum supported, as current versions of MariaDB and Percona are still based on 5.6.