pmval: improve reporting in the region of <mark> records
pmval: improve reporting in the region of <mark> records

Convoluted logic here that was confusing the attempts to diagnose
libpcp changes ... I doubt that anyone will notice any differences
in real use cases.

wuliming/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,wuliming/pcp,wuliming/pcp,adfernandes/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,wuliming/pcp,adfernandes/pcp,adfernandes/pcp,adfernandes/pcp,wuliming/pcp