added supportsReleaseSavepoints(), disabled releasing for Oracle and DB2 (already disabled for MSSQL

disable savepoints by default, added dedicated getter/setter to enable/disable, added exceptions when trying to use savepoints when not supported by the platform

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.