[2.0] DDC-169 - Further refactorings, schema max identifier length is now used for asset generation. Added platform-wide test for unique index generation with create table.

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

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

[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] Test coverage for OFFSET AND LIMIT sql generation for all platforms and Query class with setFirstResult() and setMaxResult()

divided some assertions in various cohesive methods and renamed method names to conform to agile documentation (affects #2316)

[2.0] Started to implement proxy object handling. Introduced a configuration switch for partial objects (allowPartialObjects) that defaults to TRUE. Setting to FALSE enables proxying and lazy-loading.