Update plugin/AutoClose.vim

To prevent this from happening: http://stackoverflow.com/questions/8395923/vim-configuration-throwing-errors-on-one-machine-but-not-the-other
Merge pull request #41 from lowks/patch-1

make sure vim knows the script is UTF-8 encoded (otherwise it will complain in some configurations
Close popup menu on Esc: do not feed ^E for Esc

complete_CTRL-E is different from Escape in the popup menu; Escape is
meant to close it, while CTRL-E will leave you in insert mode.