BUG: listpri picked up non-priority patterns.

The regexp for the priority wasn't anchored to the beginning of the task. (As the filtering is done inside the _list pipeline, the task number has already been prepended.)
Also, by passing the regexp directly to _list, a case-insensitive search was performed, so despite [A-Z], lowercase characters were picked up, too. Need to make use of post_filter_command to inject a separate, case-sensitive grep into the pipeline.

Bonus: Added test for highlighting of listpri command.

tests/t1250-listpri.sh

@@ -26,4 +26,46 @@ TODO: 0 of 3 tasks shown
 --
 TODO: 1 of 3 tasks shown
 EOF
+
+test_todo_session 'listpri highlighting' <<EOF
+>>> todo.sh listpri
+1 (B) smell the uppercase Roses +flowers @outside
+2 (C) notice the sunflowers
+--
+TODO: 2 of 3 tasks shown
+EOF
+
+cat > todo.txt <<EOF
+(B) smell the uppercase Roses +flowers @outside
+(C) notice the sunflowers
+(m)others will notice this
+(n) not a prioritized task
+notice the (C)opyright
+EOF
+test_todo_session 'listpri filtering' <<EOF
+>>> todo.sh -p listpri
+1 (B) smell the uppercase Roses +flowers @outside
+2 (C) notice the sunflowers
+--
+TODO: 2 of 5 tasks shown
+
+>>> todo.sh -p listpri b
+1 (B) smell the uppercase Roses +flowers @outside
+--
+TODO: 1 of 5 tasks shown
+
+>>> todo.sh -p listpri c
+2 (C) notice the sunflowers
+--
+TODO: 1 of 5 tasks shown
+
+>>> todo.sh -p listpri m
+--
+TODO: 0 of 5 tasks shown
+
+>>> todo.sh -p listpri n
+--
+TODO: 0 of 5 tasks shown
+EOF
+
 test_done