[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-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

Fixed oracle integer/boolean type detection in OracleSchemaManager::_getPortableTableColumnDefinition()

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.

DBAL-50 - Fix another follow-up bug, Index column names are not being sanitized to lower-case, which will make comparisons fail that shouldnt.

DBAL-50 - Fix bug in Postgres Schema Manager not handling column names in composite foreign keys correctly.

DBAL-50 - Fix bug in Postgres Platform not handling index column names that are comming from pg_attributes correctly

DBAL-50 - Fix two bugs occuring when new index handling is mixed with ORM (which produces an additional set of very long automatically generated identifiers) in automatic identifier name generation.

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

Fix bug in Oracle Schema/Platform detection of DateTime vs DateTimeTz type and disable a logging test that breaky MySQL testsuite.

Apply array_change_key_case in MysqlSchemaManager::_getPortableColumnDefinition() and adapt further code to work with it

DBAL-21 - Fallback for Domain Types to underyling db types when matching against Doctrine Mapping typesin Postgres Platform/SchemaManager

DBAL-22 - Fix DateTime with Timezone handling in Postgres and Oracle by introducing new type DateTimeTz and have SchemaManagers of both platforms detect this type. Added general conversion testcase which made some bugs in Oracle Date Handling and $stmt->fetchColumn() appear

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

Fixed a problem in PostgreSql AutoIncrement Detection, changed Autoincrement API for platform/schema manager interaction a little bit