Break undos when calling Isurround

[dyamon]

The idea is to change

vim-surround/plugin/surround.vim

Lines 596 to 597 in aeb9332

	inoremap <silent> <Plug>Isurround <C-R>=<SID>insert()<CR>
	inoremap <silent> <Plug>ISurround <C-R>=<SID>insert(1)<CR>

to

inoremap <silent> <Plug>Isurround  <C-G>u<C-R>=<SID>insert()<CR>
inoremap <silent> <Plug>ISurround  <C-G>u<C-R>=<SID>insert(1)<CR>

to break undos to when inserting parenthesis.

This ended up in my configs since I almost always want this behaviour instead of undoing the whole insert action.

I'm proposing this because other people might want this behaviour. If you think this is not a sensible default, feel free to close this issue.