chg: create path of output files

A modular extraction requires that the output directory exists. For each module the extraction algorithm invokes a filename generator; the string returned by this generator is the filename where the extracted code is stored. If the tool returns an error if the generator returns a filename prefixed by some path. This behavior is annoying when the driver tries to follow some package convention like in Java.

The proposed patch creates, if necessary, the prefix path of an output filename returned by the generator.