[DBAL-374] Fix issue with column quoting in primary keys, fixing this in indexes in general is much more complex as the code is messy.

DBAL-84 - Fix VARCHARs being silently set to 255 chars when larger than Maxlength. Now they are converted to Text/CLOB fields automatically. Refactored the VARCHAR code considerably.

[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-91 - Fix auto-generation of asset names (foreign keys and indexes) which could lead to exceptions due to auto-quoting of PostgreSQL for example. Now hashing the names with crc32+dechex

Revertd partially the support to DBAL\Transaction, it was wrong. Fixed implementation of ORM\EntityTransaction and fixed tests.

[2.0][DDC-92] Fixed. Patch provided by Christian Heinrich. [DDC-274] Started some method renaming. [DDC-142] Fixed (join column names and discriminator column names dont support quoting) [DDC-258] Fixed.

[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.