Checking that the platform supports foreign key is not the right case
here, because we should check if we can create them by themselves, after
the table is created. It is not the case for Sqlite.

Closes #3990

supportsSchemas() was already added (see last commit).
So changed expectation from 1 to any.

Added the supportsSchemas method in the mock because it's being used now.

default schema name is public for postgresql not default. Added debug
statements to test travis-CI.

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

DBAL-54 - Fix sequence drop executed before tables, however sequences mostly depend on tables. Also clean up several test-failures on MSSQL tests and  Oracle Index detection.

[2.0] Refactored Doctrine\DBAL\Schema API a bit Table::createColumn() was inconsistent with all the other methods being add*

[2.0] - DDC-169 - Added DropSchemaSql Visitor - Refactored Visitor package a bit, however its still not very appealing to have that much use statements cluttered in the code

[2.0] - DDC-169 - Began refactoring of DBAL code, introduced object notation for a database schema, including Tables, Indexes, Constraints, Sequences and Columns. Added a CreateSql Visitor which transforms a schema object graph into the required SQL statements to create it. Next: Replacing SchemaTool::getCreateSql() with new syntax...