List files to modify.

Explicitely list the files to modify when upping/checking the VERSION
of the various CoreList modules, for easy copy-and-pasting.

I grew tired of running find.
Update Module::CoreList for 5.21.5
Use F<> for files, not L<>
List updated modules in perldelta
Update acknowledgements in perldelta
Be consistent when it comes to (not) terminating =heads with a period.
Added 5.21.5 release to perlhist