Remember to close temporary connection in PostgreSqlSchemaManager::dropDatabase() and PostgreSqlSchemaManager::createDatabase()

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.

Unsigned column properties were never set. In consequence all migrations diff were trying to change the column definition when it was already changed.

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

Renamed AbstractAsset#isQuoted to #isIdentifierQuoted. Added new public method isQuoted that returns AbstractAsset

[DBAL-166] Default MySQL to UTF8/utf8_general_ci. Allow to set default table options from SchemaConfig.

[DBAL-237] Fix bug when removing and adding an index on the same columns that may be part of a foreign key.

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

This is necessary because pdo_sqlsrv still has some little bugs that
prevent it from being used in all use-cases. Additionally only sqlsrv
can make use of the Azure federations features.