autojump plugin enhanced

plugins/autojump/autojump.plugin.zsh

-if [ -f /opt/local/etc/profile.d/autojump.sh ]; then
-  . /opt/local/etc/profile.d/autojump.sh
-elif [ -f `brew --prefix`/etc/autojump ]; then
+if [ -f /usr/share/autojump/autojump.zsh ]; then # debian and ubuntu package
+  . /usr/share/autojump/autojump.zsh
+elif [ -f /etc/profile.d/autojump.zsh ]; then # manual installation
+  . /etc/profile.d/autojump.zsh
+elif (`command -v brew >/dev/null`); then # mac os x with brew
+  if [ -f `brew --prefix`/etc/autojump ]; then
     . `brew --prefix`/etc/autojump
+  fi
 fi