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