This coherent with what is done for Table. All platform specific things
are grouped into an options array. Eventually flags should be migrated
into options as well.

Support for Partial Indexes was available in Doctrine 1 following
http://www.doctrine-project.org/jira/browse/DC-82. This commit
reintroduce support for Doctrine 2. We use the same syntax with an
optionnal "where" attribute for Index and UniqueConstraint.

improved sqlserver 'doModifyLimitQuery' select-from pattern

with assertEquals

Allow to connect without a dbname param

The PDO connection allow the instantiation of the connection even if the dbname
parameter isn't present. This change is there to make sure both behave the same way.

Fix pg boolean conversion

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.