Base rbenv plugin on the rbenv in the path.

Rather than do our own searching, this gives the user full control of
the PATH variable and of the search order for rbenv.  It's also probably
faster, since we let zsh do the searching for us.

plugins/rbenv/rbenv.plugin.zsh

@@ -1,9 +1,5 @@
-FOUND_RBENV=0
-for rbenvdir in "$HOME/.rbenv" "/usr/local/rbenv" "/opt/rbenv" ; do
-  if [ -d $rbenvdir/bin -a $FOUND_RBENV -eq 0 ] ; then
-    FOUND_RBENV=1
-    export RBENV_ROOT=$rbenvdir
-    export PATH=${rbenvdir}/bin:$PATH
+if [[ $+commands[rbenv] -eq 1 ]] ; then
+
   eval "$(rbenv init -)"
 
   alias rubies="rbenv versions"
@@ -33,11 +29,8 @@ for rbenvdir in "$HOME/.rbenv" "/usr/local/rbenv" "/opt/rbenv" ; do
       echo "$(current_ruby)"
     fi
   }
-  fi
-done
-unset rbenvdir
 
-if [ $FOUND_RBENV -eq 0 ] ; then
+else
   alias rubies='ruby -v'
   function gemsets() { echo 'not supported' }
   function rbenv_prompt_info() { echo "system: $(ruby -v | cut -f-2 -d ' ')" }