In some cases the Comparator class returns multiple drops for the same foreign key.
Specifically, in case you have two tables, A & B, with A having a foreign key FK
referencing B, if you drop table B, the resulting diff shows this FK twice,
once on the diff->orphanedForeignKeys array as we're deleting B, and another on
the diff->changedTables array as table A is also being modified. As a result of this you
get the DROP FOREIGN KEY instruction twice in the final SQL.

[DDC-1657] Prevent autoincrement sequences from creating DROP SEQUENCE statements because of old/new schema missmatch.

DDC-451 - GUID support through a specific GUID Type, SQL Server specific implementation all others fallback to Varchar fields, no automatic default value = new guid support yet.

[DBAL-220] Add support for Index flags and implement support for SQL Server CLUSTERED/NONCLUSTERED and MySQL FULLTEXT.

[DBAL-204] Sane refactoring of the previous idea. Removed a bunch of code again and implemented proper schema namespacing. Also got the wording right (hopefully) and fixed the algorithms.

DBAL-132 - Make Table::addUnnamedForeignKeyConstraint() generate a name based on the input, @deprecated addUnnamedForeignKeyConstraint and addNamedForeignKeyConstraint.

DBAL-112, DBAL-113 - Implement AbstractPlatform::getAlterSequenceSQL() and fix comparator code for sequences

Fix bug in DropSchemaSQLCollector dropping tables before sequences which can cause constraint errors

DBAL-91 - Fix auto-generation of asset names (foreign keys and indexes) which could lead to exceptions due to auto-quoting of PostgreSQL for example. Now hashing the names with crc32+dechex