bsd-spell: Install as bspell instead of spell

Install bsd-spell as bspell instead of spell since it otherwise
conflicts with textproc/aspell-ispell.

While here switch to pkg-plist for the pkg content listing.

PR: 274217
Reviewed by: fernape
Tested by: fernape
Approved by: fernape
Differential Revision: https://reviews.freebsd.org/D43083