If a PRIMARY KEY field is defined in sqlite without autoincrement then
keys might be reused when rows are deleted, explicitly settings autoincrement
will prevent this.

Autoincrement is not enabled by default due to additional overhead introduced
with autoincrement bookkeeping and should only be enabled when the additional
uniqueness is required.

The SQLite and Oracle platforms produces a `ROUND()`'ed or `TRUNC()`'ated difference between the datetimes. However it should be the difference between dates.

It is a somewhat fragile thing to do.

Fix PSR2 rules : "As per PSR2, the static declaration should come after the visibility declaration."

 Closes #2436

fixes #2270

While technically it could work, the schema introspection of Sqlite
platform has severe flaws preventing us to provide reliable support
of partial (and non-partial) indexes for the moment.

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.

See symfony/symfony#10238