mysql-connections in cache adapters: use a seperate connection to avoid nested transactions

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@4246 1f8fe7d8-47f0-464c-8d0a-336f4953ab05
build auto version (3065) ...

git-svn-id: http://www.pimcore.org/svn/pimcore/private/core/trunk@4247 1f8fe7d8-47f0-464c-8d0a-336f4953ab05