Disable bracketed-paste-magic in zsh 5.1.1, where it is buggy

A bracketed-paste-magic bug breaks pasting of CJK and some other characters in zsh 5.1.1.
http://www.zsh.org/mla/workers/2015/msg02680.html
See #4434

lib/misc.zsh

@@ -1,14 +1,19 @@
 ## Load smart urls if available
-for d in $fpath; do
+# bracketed-paste-magic is known buggy in zsh 5.1.1 (only), so skip it there; see #4434
+autoload -Uz is-at-least
+if [[ $ZSH_VERSION != 5.1.1 ]]; then
+  for d in $fpath; do
   	if [[ -e "$d/url-quote-magic" ]]; then
-		if [[ -e "$d/bracketed-paste-magic" ]]; then
+  		if is-at-least 5.1; then
   			autoload -Uz bracketed-paste-magic
   			zle -N bracketed-paste bracketed-paste-magic
   		fi
-		autoload -U url-quote-magic
+  		autoload -Uz url-quote-magic
   		zle -N self-insert url-quote-magic
+      break
   	fi
-done
+  done
+fi
 
 ## jobs
 setopt long_list_jobs
@@ -22,8 +27,7 @@ alias _='sudo'
 alias please='sudo'
 
 ## more intelligent acking for ubuntu users
-if which ack-grep &> /dev/null;
-then
+if which ack-grep &> /dev/null; then
   alias afind='ack-grep -il'
 else
   alias afind='ack -il'