podwrapper: Give an error if an --insert or --verbatim pattern is not found in the input.
generator: Generate copyright notice in generated POD fragments.

Using =begin comment ... =end comment.
po-docs: There are no *.pl files in the po-docs subdirectories any longer.
po-docs: Filter the po4a warning and =encoding line.
podwrapper: Remove =encoding from input files and add it back in podwrapper.

This changes podwrapper so that the input (POD) files should not
contain an =encoding directive.  However they must be UTF-8.
Podwrapper then adds the '=encoding utf8' directive back during final
generation.

This in particular avoids problems with nested =encoding directives in
fragments.  These break POD, and are undesirable anyway.