[DBAL-45] Add reserved keywords feature through platforms and as a validator for any Schema instance with subelements. Add Command to check for reserved keywords in current database.

DBAL-88 - Change index retrieval of MySQL to use information_schema.statistics which avoids errors when using reserved words for table names (for example in database driver).

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-62 - There is a diference between maximum length (now 4000, oracle is the smallest possible denominator here) of varchars and the default length (255).

This reverts commit 3b79401b to allow a sane merge of Juokaz patch.

DBAL-54 - Fix sequence drop executed before tables, however sequences mostly depend on tables. Also clean up several test-failures on MSSQL tests and  Oracle Index detection.

Signed-off-by: Juozas Kaziukenas <juozas@juokaz.com>

Signed-off-by: Juozas Kaziukenas <juozas@juokaz.com>