Support for Partial Indexes for PostgreSql and Sqlite

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.
Fix code style as mentionned in PR comments
Refactor partial into options array

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.
Fix more code style as mentionned in PR comments
Surround ! with spaces according to code style
Compete BC notice with addUniqueIndex()
Cover Index options with unit tests
Deactivate partial index support for Sqlite

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.
Hotfix for DBAL-669

Updating a schema should introduce also schema creation statements in the generated SQL
add ability to introspect namespace names on capable platforms
fix assumption that SQL Anywhere supports schemas
revert platform check for schemas needing creation
create namespaces in schema explicitly
Merge pull request #444 from doctrine/hotfix/DBAL-669

DBAL-669 - Update SQL generated by the schema tool will also create schemas
Merge pull request #600 from PowerKiKi/feature-partial-indexes

Support for Partial Indexes for PostgreSql and Sqlite
Allow current timestamp default to be specified for DateTimeTz type.
Added unit test for DateTime/DateTimeTz default timestamps; made same change for SQL server.
Splitting second test into its own test method.
Made the checks consistent using in_array.
#662 - minor cs fixes (spaces)