CONTRIB-11: Do not quote constraint condition in ora:addCheck

I created a maintenance branch for version 1.2.x restoring the files to the state of https://liquibase.jira.com/svn/CONTRIB/trunk/oracle-extensions/trunk@2078.

The fix for [CONTRIB-11](https://liquibase.jira.com/browse/CONTRIB-11) itself is very simple. Without it `ora:addCheck` produces invalid SQL statements.