[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.

This will only happen when adding primary keys via ALTER TABLE

- Fixing issue, key name corrected

In some cases the Comparator class returns multiple drops for the same foreign key.
Specifically, in case you have two tables, A & B, with A having a foreign key FK
referencing B, if you drop table B, the resulting diff shows this FK twice,
once on the diff->orphanedForeignKeys array as we're deleting B, and another on
the diff->changedTables array as table A is also being modified. As a result of this you
get the DROP FOREIGN KEY instruction twice in the final SQL.

[DBAL-335] Fix nasty bug in MasterSlaveConnection, connecting and writing to slave when using keepSlave option.

Bugfix DDC-2013 - Default Session Value ".," for "NLS_NUMERIC_CHARACTERS". This is needed because Oracle uses other characters for decimal separation depending on the servers locale

Default table collation changed to `utf8_unicode_ci`, as it handles properly a much wider array of characters (Cyrillic, for example) at a generally negligible cost of performance.