Hope this will make people using feed_command less likely: this hides bugs.
Already found at least two:
1. msgpackparse() will show internal error: hash_add() in case of duplicate
keys, though it will still work correctly. Currently silenced.
2. ttimeoutlen was spelled incorrectly, resulting in option not being set when
expected. Test was still functioning somehow though. Currently fixed.
Also make setpos("'A", [999, 1, 1, 0]) fail, i.e. return -1 (assuming there is no buffer 999).
Fixes#5713
Background:
`:help setpos()` mentions an argument `"bufnum"` that determines the buffer a mark should be put in.
This argument is respected for uppercase marks, but not for lowercase marks.
This is reasonable (though I personally would like `setpos()` to be able to set marks in other buffers), but the help doesn't mention this anywhere.
It's also strange that attempting to change buffers with `setpos('.', [bufnr('#'), 1, 1, 0])` alerts the user that having a different buffer is an error, while attempting to set a mark with `setpos("'d", [bufnr('#'), 1, 1, 0])` doesn't tell the user that the `"bufnum"` argument is an error.
