[DBAL-1063] Allow defining duplicate indexes on a table

PostgreSQL needs explicitly closed connection in functional test

Fixed typo

[DBAL-1097] Fix foreign key constraint referential action on Oracle

[DBAL-1087] Length of fixed string type (char) is ignored on Postgre schema update

Close #751

Fix error handling in mysqli driver

[DBAL-1095] Fix index introspection on SQL Anywhere

Fix creating and dropping database on PostgreSQL

Cleanup travis database creation

[DBAL-1062] Fix renaming indexes used by foreign key constraints

[DBAL-1090] Changing string to fixed string is not recognized in PostgreSQL Platform

Take care about mariadb platform

Added doModifyLimitQuery for SQLServer2012Platform that uses OFFSET... FETCH

Simplified doModifyLimitQuery per @deeky666 comments, added test case for orderby with parenthetical expression

minor phpdoc fixes in the schema files

minor phpdoc fixes in the platform files

Removed non-phpdoc @internal tags