let g:vimrplugin_assign = 2 swaps precedence of '_' and '<-'

This modification allows the swapping of precedence between '_' and '<-' when g:vimrplugin_assign == 2.

The behavior is as follows:
- Insertion of '_' after a '_' changes it to ' <- '
- Insertion of '_' after a ' <- ' replaces it with '__'
Else:
- Insertion of '_' leaves '_'

Thanks!

Harold