The quotes are definitely not the way to go. I've tried
vim -u test_vimrc.vim
where test_vimrc.vim contained merely your first line (slightly
modified):
nnoremap <f3> :set nobackup<return>
and it worked fine. I don't know whether it has to do with
switching over to nnoremap (I prefer to be explicit when I
specify a mapping) or some other plugin that is overriding your
desired settings. You might try
:scriptnames
to see what scripts are being loaded (and may want to investigate
them in the event that one of them is rebinding <f3>).
-tim
Thanks for your gnawing on this. As it turns out, and I had responded thusly
to another good soul, the problem was merely my method of evoking my intended
change:
source ~/.vimrc
That DIDN'T work!
What I had done (to begin) was borrow an already valid keymapping:
map <silent> <F2> :nohlsearch <return>
and copied it to use as a template (it worked once...oughta work again)
the change became (and it ultimately worked),
map <F3> :set nobkackup <return> #bTW, <return> becomes <CR> when :map
my problem was, the shell command <source ~/.vimrc> was the wrong way to go-it
created problems. As soon as I logged out and back in, everything worked fine.
