Issue 4894: Remove unescaped @funindex entries

Issue 4894: Remove unescaped @funindex entries

With adjacent @funindex entries of which one differs from the other
only by the absence of a preceding backslash, the one without the
preceding backslash is removed.  This is done by using the script:

    sed -i '/^@funindex/{N;s/^@funindex \\\([^\n\\]*\)\n@funindex \1$/@funindex \\\1/mg;s/^@funindex \([^\n\\]*\)\n@funindex \\\1$/@funindex \\\1/mg;P;D;}' $(git grep -l '^@funindex')