completion: don't autocorrect too many errors

Otherwise, we could complete to just any word.
paste: add a snippet to do "safe" paste

See:
 https://github.com/robbyrussell/oh-my-zsh/pull/1698
 http://thejh.net/misc/website-terminal-copy-paste
 http://www.ush.it/team/ascii/hack-tricks_253C_CCC2008/wysinwyc/what_you_see_is_not_what_you_copy.txt

This is still not safe but useful for accidental copy/paste
zsh: remove anonymous "__" function