Fix #DBAL-615 - ALTER with reserved keywords

PR #302 introduced platform quoting for manipulation of PK, FK and indexes. Alter queries are left unquoted, which means that ALTER with table names that happen to be reserved platform keywords, will fail.
For example:
`````sql
ALTER TABLE order DROP FOREIGN KEY FK_F5299398D5289B7F;
ALTER TABLE set DROP FOREIGN KEY FK_E61425DC1BF22D93;
ALTER TABLE storage ADD CONSTRAINT FK_547A1B3487068541 FOREIGN KEY (`addressId`) REFERENCES `address` (`id`);
````
http://www.doctrine-project.org/jira/browse/DBAL-615