(todo-merge-category): Fix implementation to make merging to a
category in another file work as documented. Eliminate now
insufficient and unnecessary renaming of archive category, correct
document string accordingly, and clarify it. If the numerically
last category of the source file was merged, make the first
(todo-merge-category): Fix implementation to make merging to a
category in another file work as documented. Eliminate now
insufficient and unnecessary renaming of archive category, correct
document string accordingly, and clarify it. If the numerically
last category of the source file was merged, make the first