Do not disable less' alternate screen, close #35

While the '-X' switch allows the user to quit less with the relevant
portion of a man page still visible, it breaks mouse scrolling.

environment.zsh

@@ -93,7 +93,7 @@ fi
 export LESSCHARSET="UTF-8"
 export LESSHISTFILE='-'
 export LESSEDIT='vim ?lm+%lm. %f'
-export LESS='-F -g -i -M -R -S -w -X -z-4'
+export LESS='-F -g -i -M -R -S -w -z-4'
 
 if (( $+commands[lesspipe.sh] )); then
   export LESSOPEN='| /usr/bin/env lesspipe.sh %s 2>&-'