Updating a schema should introduce also schema creation statements in the generated SQL

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.

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

Temporary fix for issues appearing due to DBAL-2 reopening, found an actual additional bug that is now fixed in PostgresSQL Schema Manager

Fix change to Postgresql NULL Column detection

Temporary fix for issues appearing due to DBAL-2 reopening, found an actual additional bug that is now fixed in PostgresSQL Schema Manager

[2.0] DDC-396 - Fixed bug with RESTRICT/NO ACTION and PHP NULL not valued as the same in Schema Foreign Key Diff

[2.0] DDC-312 - Revert annoying View and Trigger variables in Schema instance, complete "View" support by just returning a View instance