Performance enhancement for lib/grep

- Use $ZSH_CACHE_DIR to store the grep alias with all the right features
- Expire the cache after 24 hours
- See issue #8444

lib/grep.zsh

@@ -1,3 +1,8 @@
+# see if we already cached the grep alias in past day
+_grep_alias_cache=("$ZSH_CACHE_DIR"/grep_alias.zsh(Nm-24))
+if (( $#_grep_alias_cache )); then
+    source "$ZSH_CACHE_DIR"/grep_alias.zsh
+else
     # is x grep argument available?
     grep-flag-available() {
         echo | grep $1 "" >/dev/null 2>&1
@@ -19,11 +24,17 @@ elif grep-flag-available --exclude=.cvs; then
         GREP_OPTIONS+=" --exclude=$EXC_FOLDERS"
     fi
 
+    {
         # export grep, egrep and fgrep settings
-alias grep="grep $GREP_OPTIONS"
+        echo alias grep="'grep $GREP_OPTIONS'"
-alias egrep="egrep $GREP_OPTIONS"
+        echo alias egrep="'egrep $GREP_OPTIONS'"
-alias fgrep="fgrep $GREP_OPTIONS"
+        echo alias fgrep="'fgrep $GREP_OPTIONS'"
+    } > "$ZSH_CACHE_DIR/grep_alias.zsh"
+
+    source "$ZSH_CACHE_DIR/grep_alias.zsh"
 
     # clean up
     unset GREP_OPTIONS EXC_FOLDERS
     unfunction grep-flag-available
+fi
+unset _grep_alias_cache