- fixes platform's COMMENT ON statement support
- implements reverse engineering for column comments
- marks boolean column type commented for distinction

fixes #2182

[2.0] DDC-313 - Removed abstracted trigger support, list functions, list users and the platform specific code to generate the queries for this stuff.

[2.0] DDC-312 -  Refactored View support of all platforms a little - Oracle now also supports the retrieval of the sql used to generate a view so that a common datastructure View is a viable option.

[2.0] DDC-302 - Drop convenience methods since their API is somewhat strange, have to think about something else. Dropped AbstractSchemaManager::listTableConstraints() support - since it only returns the names of all constraints, which are already returned much more nicely with listTableIndexes().

[2.0] DDC-169 - Fix build, Postgres, Oracle and Sqlite made some minor troubles with regards to sequences.

[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] Fixed DDC-63 and DDC-106. Oracle tests for SchemaManager need further tweeking, marked as skipped for now.

[2.0] DDC-91 - Enhanced SchemaManager::listTableIndexes() considerably. Add primary keys to the index list, add a bool flag primary to each index, add an array of columns to each index. Moved a test to SchemaFunctionalTestCase to check that every database (Mysql, Pgsql, Sqlite, Oracle) returns exactly the same data from this function.

[2.0] DBAL cleanups (DDC-46). Proxy class improvements (DDC-19, DDC-39). Started new UPGRADE_TO document for upgrade instructions between advancing Doctrine 2 versions.

[2.0] Added functionality to convert a Doctrine 1 schema to Doctrine 2 to help users with upgrading. Lots of other small bug fixes and changes.

[2.0] Introduced SQL logging facilities. Made Type constructor private to prevent instantiation and force use of the factory method getType().

[2.0] More general work on the SchemaManager and Platform classes. Making API more complete and adding sqlite and mysql test coverage.