Revert "Clang WaE: -Woverloaded-virtual weirdness, this seems to help"
as that broke tinderboxes. Try another way instead, renaming two
versions of the overloaded render() method, so that there is no longer
any overloading.

Compiles -Werror-clean with Clang, hopefully no problem with other
compilers either.

This reverts commit 86b99ab4.