[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-169 - Stripped case handling since its just a load of complex crap and doesn't solve any problem! Idea: just implement case-insensitivity in the comparator.

[2.0] DDC-169 - Introduced handling of schema / database case-sensitivity differences and to allow compability between different platforms.

[2.0] DDC-169 - Changed AbstractPlatform and AbstractSchemaManager Constraint API to accept Constraint interface, which is implemented by indexes and foreign keys.

[2.0] DDC-169 - Converted introspection queries of all platforms to return Column, Sequence, Index, ForeignKey Schema Instances instead of arrays, heavily pimped Oracle support thereby.

[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...