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Previously the patchfiles were copied into the source of each
generated parser, even though they are identical for all parsers and
always use a hardcoded package name. This means that all generated
parsers had conflicting classes, although in practice this was not
noticeable, because the classes were always identical.

These common files are now a proper separate library that all
generated parsers will depend on. This will fix the class name
conflicts when using more than one SableCC parser in a single project.