nls: Update the man-po logic

nls: Update the man-po logic

Put the man-po pot file under version control like its po/*.pot sibling.

Makefile now auto-matically generates the list of man pages as they are
in a single directory. There were some missing!

pot file target is dependent on the untranslated man pages

When downloading from translation project, run po4a to sync the new
po files correctly.

Downloaded man po files from translation project and synched.

Thanks to @gorean for the info

References:
 procps-ng/procps#258

Signed-off-by: Craig Small <csmall@dropbear.xyz>