Bug Fix: prepend not correct on prioritized tasks

Check for priority, if one exists, remove, prepend and add back.
If priority doesn't exist just runs the normal prepend functionality.

tests/t1400-prepend.sh

@@ -0,0 +1,55 @@
+#!/bin/sh
+
+test_description='basic prepend functionality
+'
+. ./test-lib.sh
+
+test_todo_session 'prepend usage' <<EOF
+>>> todo.sh prepend B B
+usage: todo.sh prepend ITEM# "TEXT TO PREPEND"
+=== 1
+EOF
+
+cat > todo.txt <<EOF
+(B) smell the uppercase Roses +flowers @outside
+notice the sunflowers
+stop
+EOF
+test_todo_session 'basic prepend' <<EOF
+>>> todo.sh list
+1 (B) smell the uppercase Roses +flowers @outside
+2 notice the sunflowers
+3 stop
+--
+TODO: 3 of 3 tasks shown from $HOME/todo.txt
+
+>>> todo.sh -p list
+1 (B) smell the uppercase Roses +flowers @outside
+2 notice the sunflowers
+3 stop
+--
+TODO: 3 of 3 tasks shown from $HOME/todo.txt
+
+>>> todo.sh prepend 2 test
+2: test notice the sunflowers
+
+>>> todo.sh -p list
+1 (B) smell the uppercase Roses +flowers @outside
+3 stop
+2 test notice the sunflowers
+--
+TODO: 3 of 3 tasks shown from $HOME/todo.txt
+
+>>> todo.sh prepend 1 test
+1: (B) test smell the uppercase Roses +flowers @outside
+
+>>> todo.sh -p list
+1 (B) test smell the uppercase Roses +flowers @outside
+3 stop
+2 test notice the sunflowers
+--
+TODO: 3 of 3 tasks shown from $HOME/todo.txt
+
+EOF
+
+test_done