Fix missing PF_NO_MANA in get_pflag_desc()

While I was at it, I also moved the descriptions to list-player-flags.h
to keep things DRY and to hopefully prevent similar issues in the future.
Merge pull request #374 from BardurArantsson/restruct-fix-missing-pflag

Fix missing PF_NO_MANA in get_pflag_desc()