Fix export syntax of $GREP_OPTIONS

Fixes #2641, #2642

lib/grep.zsh

@@ -8,5 +8,6 @@ GREP_OPTIONS=
 for PATTERN in .cvs .git .hg .svn; do
     GREP_OPTIONS+="--exclude-dir=$PATTERN "
 done
-export GREP_OPTIONS+='--color=auto '
-export GREP_COLOR='1;32'
+GREP_OPTIONS+="--color=auto"
+export GREP_OPTIONS="$GREP_OPTIONS"
+export GREP_COLOR='1;32'