as I promised I now send some questions to you. Let's move step-by-step.
4615--4633: what means '%REWRITTEN%' in sed_rewrite_old_files and sed_rewrite_new_files? Is this just a part of name? If yes, why can not we just add suffix like '.tmp' instead of prefix that contains special symbols?
4635--4653: we echo directories which were specified by user. $sourcebase, $m4base and $auxdir are the necessary directories. $docbase will be echoed only if we have at least one file which name starts with 'doc/'. $testsbase will be echoed only if we have at least one testflag enabled. But what happens at lines 4649--4652?
4670--4685: as I understand here we just save tables of files. However, to understand this table I need your explanations on lines 4615--4633 (see above). 4687--4699: we take first column from each file (see 4670--4685) and combine these two lists into one big list. Then from this big we delete duplicated files.
Thank you for your help and patience. The nearest code seems to be clear, at least at the first look. :-)