Merge pull request #801 from kalos/autojump

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
-  . `brew --prefix`/etc/autojump
+if [ $commands[autojump] ]; then # check if autojump is installed
+  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 [ $commands[brew] -a -f `brew --prefix`/etc/autojump ]; then # mac os x with brew
+    . `brew --prefix`/etc/autojump
+  fi
 fi