[DBAL-1022] Wrap PDOException in PDOConnection::exec()

Enabled placeholders for "in" method in ExpressionBuilder

doModifyLimitQuery() was missing an outer "ORDER BY doctrine_rownum"

Close #654

[DBAL-1004] Fix generating COMMENT ON COLUMN statements for quoted identifiers

Close #685
Close #688
Close #691

Close #688

Close #691

[DBAL-1016] Fix explicitly quoted table identifiers in ALTER TABLE statements

Adds support for setting the charset in SQLSrv

As seen here => http://technet.microsoft.com/en-us/library/cc626307(v=sql.105).aspx

Reset date fields to UNIX epoch in TimeType.

TimeType resets date fields (i.e. unused DateTime object fields) to UNIX
epoch (1970-01-01). This makes TIME field mapping stabe (i.e. same time
will be always mapped to the same DateTime fields).

See DDC-179 (similar issue with DateType). Fixes DBAL-993.

[DBAL-1014] Support HHVM mysqli driver

Close #696

[DBAL-1009] Fix column comment lifecycle

[DBAL-1001] Fix NULL / NOT NULL clause for column alterations in Oracle

[DBAL-831] Fix explicit case sensitive identifiers in Oracle

[Documentation] Add missing quotes at the end of literal strings