Added possibility to apply "LIMIT 0" in PostgreSQL adapter

This is possible in Postgres and may be useful. "OFFSET 0" seems useless but I think it should be added for consistency.
fix failed jekyl compilation due to highlight tags
Merge pull request #419 from lunika/master

 	fix failed jekyl compilation due to highlight tags
change default locale from en_EN to en_US
Merge pull request #420 from lunika/default_locale

change default locale from en_EN to en_US
allow to use reference-only on external-schema tag
don't generate sql if skipSql equal true on parent table
on versionnable behavior, don't generate sql if parent table had skipSql
equal to true
create test for I18n behavior testing skipSql parameter
create test for Versionnable behavior, testing skipSql parameter
Merge pull request #422 from lunika/master

I18n, versionnable and external-schema fix issue
Use symfony/validator 2.2.*@dev as long as the fix for issue #427 is open.
Added for `namespaced` schema a tablePrexis, otherwise it will overwrite the table from `bookstore`.
Fixed typo
Print now the SQL in the exception in sql:insert command when it fails. Better for debugging.
Added some docBlocks. Added a check against `->getDatabase` before accessing it in getForeignTable().
Added `hasColumn` and some docBlocks.
Added isUnique to Model\Table and some docBlocks.
PostgreSQL requires the keys of the foreignTable of a foreignKeys to be unique.
Fixed missing `use`.