Unset the MACTEXT_PATH var so it doesn't leak through to env

Thought this variable wasn't making it to the session, but it does even
without the `export`.  This corrects that by explicitly unsetting it
before we continue.

plugins/latex.plugin.bash

@@ -5,3 +5,4 @@ MACTEX_PATH=/usr/local/texlive/2009/bin/universal-darwin
 if [[ -d  $MACTEX_PATH ]]; then
     export PATH=$PATH:$MACTEX_PATH
 fi
+unset MACTEX_PATH