Indentifiers are not quoted in queries build for Nested Relations (patch included)

It was OK using reserved words as column names before I started using Nested Relations: queries started to fail because Doctrine_Core::ATTR_QUOTE_IDENTIFIER is ignored by query builder for Nested Relations.

I solved this problem by wrapping identifiers with Doctrine_Formatter::quoteIdentifier() in several places. I'm providing a patch for your to review and commit.

Thanks.