set constant_result of empty containers created in ConstantFolding transform
mark node position in C file when starting to generate the node's code, not that of the subexpressions

--HG--
extra : amend_source : 566ce3ed6bd0efbb075126a6c5823b773c72d2ea
minor code cleanup

--HG--
extra : amend_source : c948151354a77be026c92d57abc151e51fb271c6
generate separate C code branches for each exit case of a try-finally statement
changelog
extend test
fix C compiler warning about unused variable