conditionally define t()

if user has installed the todo plugin, forego defining the 'one thing'
todo function t().

plugins/available/base.plugin.bash

@@ -137,6 +137,21 @@ usage ()
     fi
 }
 
+if [ ! -e $BASH_IT/plugins/enabled/todo.plugin.bash ]; then
+# if user has installed todo plugin, skip this...
+    t ()
+    {
+        about 'one thing todo'
+        param 'if not set, display todo item'
+        param '1: todo text'
+        if [[ "$*" == "" ]] ; then
+            cat ~/.t
+        else
+            echo "$*" > ~/.t
+        fi
+    }
+fi
+
 command_exists ()
 {
     about checks for existence of a command