plpgsql_check_function - rebase for 9.3

Hello

I am sending lightly refreshed patch for checking plpgsql functions..

I checked different implementation, but without success: a) enhancing
of SPI to some fake mode can has negative impact on application, and
patch was not clear, b) generic plpgsql walker doesn't save lines too.

I invite any ideas how to improve this patch

Regards

Pavel