Update AbstractPlatform.php

Default Boolean conversion behaviour
Update PostgreSqlPlatform.php

added postgresql literals to Boolean conversion
Update BooleanType.php

Changed to call platform specific Boolean conversion
Update AbstractPostgreSqlPlatformTestCase.php

added postgresql platform conversion test
Update PostgreSqlPlatform.php

fixed bug when $item was set as bool true value
added 'off' literal
Update AbstractPostgreSqlPlatformTestCase.php

added literals off and on to the testcase
Update PostgreSqlPlatform.php

Changes after Ocramius comments
Update PostgreSqlPlatform.php

fixed parameter order in conditions
Update AbstractPlatform.php

Description fix
Update PostgreSqlPlatform.php
Update PostgreSqlPlatform.php
Update PostgreSqlPlatform.php

updated convert function  to include uppercased values
Update AbstractPostgreSqlPlatformTestCase.php

Updated test for uppercased values
Update PostgreSqlPlatform.php
Update AbstractPlatform.php
Update AbstractPlatform.php

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.
Working on PostgreSQL incorrect boolean handling when emulating prepared statements
Complying with Doctrine PSR exceptions
'Unbreaking' public API
Applying requested fixes