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

[DBAL-42] Optimized column comment change detection. Ignore from columns with a null comment which indicates not set compared to an empty string which says delete comment.

[DBAL-42] Add support to reverse engineer Comments from MySQL, PostgreSQL and ORacle into Doctrine\DBAL\Schema\Column instances and added comment comparison into Comparator.

DBAL-50 - Explicitly add an index for each foreign key added to a Schema\Table instance. Removed code to FixSchema based on foreign keys, since assumptions now dont apply anymore. Refactored algorithms to check for duplicate or potential overrule indexes into Schema\Index classes, added tests and unified Table API handling these conflicts

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-214, DDC-303, DDC-304 - Fix several errors with Schema Inference from Database and Metadata and Comparisons, aswell as related bugs in DatabaseDriver. DDC-305 - Abstracted TRUNCATE command for all platforms.

[2.0] DDC-169 - Finished ALTER Table TableDiff refactoring, adding code to handle index and FK changes. Added a general functional test for alter table against all platforms.

[2.0] DDC-169 - AbstractPlatform::getAlterTableSql() now accepts only a TableDiff instance as argument across all platforms.

[2.0] DDC-169 - Add functionality to detect that an add + drop column diff is actually just a rename column.

[2.0] DDC-169 - Changed AbstractPlatform and AbstractSchemaManager and children to accept Table, Index and ForeignKey instances for the respective create*() methods.

[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 - Finalized implementation of Schema diff algorithm, added diffs of sequences and foreign keys. Fixed several bugs and changed the API of the Schema objects.

[2.0] - DDC-169 - Fixed another regression in refactored SchemaTool, began porting of eZ Components Database Schema Comparator, SchemaDiff and TableDiff.