[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.

Based on whether we are on 32 or 64 bit platform, postgres will return a string or an int for the expected php type of a bigint that is > 32 bits.

Use dropAndCreateDatabase schema manager function in test initialization instead of individual versions of each.

Changed 'implements' by 'extends' because AbstractSchemaSynchronizer is a class not an interface (and Eclipse PDT shows a warning that say that "The type SQLAzureFederationsSynchronizer must implement the inherited method processSqlSafely, processSql" but those methods are already implemented on AbstractSchemaSynchronizer).

Unsigned column properties were never set. In consequence all migrations diff were trying to change the column definition when it was already changed.