Improve completion

[miyakogi]

Omni-completion fails in some cases.

Example of bad case

Use this minimum .vimrc (save as compl.vim).

" Load nimrod.vim
set runtimepath+=~/.vim/bundle/nimrod.vim
filetype plugin indent on
syntax on

And open the following nim file (save as compl.nim).

type
  Socket* = object of RootObj
    FHost: int
    ab: int
    acdf: int
    aa: int
    aavv: string
    sasd: int

var s: Socket
echo s.a

vim -u compl.vim -N compl.nim

At the end of the last line, press <C-x><C-o>.

This is a screen shot. The result of completions is invalid, since the existing word "a" is ignored.

After applying changes of this PR.

Do same as above. This is a screen shot.

Regards