add dvorak-friendly aliases for frequent ls(1)-ing
make simple backup aliases allow a trailing slash

$ bam ref/
mv: cannot move ‘ref/’ to a subdirectory of itself, ‘ref/.bak’
exit 1

$ bum ref.bak/
mv: cannot move ‘ref.bak/’ to a subdirectory of itself, ‘ref.bak/ref.bak’
exit 1