PG specific attribute PDO::PGSQL_ATTR_DISABLE_NATIVE_PREPARED_STATEMENT is now only set when it is still supported

reverted @deeky666 suggestion. Since it failed on testBooleanNullConvertsToPHPValue test. 
with message Failed asserting that true is null.
Since I moved this code from BoolenType::convertToPHPValue in the first place, I presume the code there correct.

Updated test for uppercased values

updated convert function  to include uppercased values

Description fix

fixed parameter order in conditions

Changes after Ocramius comments

added literals off and on to the testcase

fixed bug when $item was set as bool true value
added 'off' literal

added postgresql platform conversion test

Changed to call platform specific Boolean conversion

added postgresql literals to Boolean conversion

Default Boolean conversion behaviour

[DBAL-807] Respect schema when renaming indexes

[DBAL-918] Correcting the doc because mysqli doesn't support named parameter natively