Match TODO keywords case-sensitively

Match TODO keywords case-sensitively

Samuel Wales writes:

> I found three places where the lowercase version of a todo
> kw is treated specially in the latest org.  For example,
>
>  * todo this is lowercase
>
> First, in the agenda, they have a special face.
>
> Second, when inserting an id link, they are removed.
>
> Third, when printing the olpath, they are removed.  To
> reproduce, place point at bol on 5 and press the spacebar.
> I expect todo to be in the olpath, but it is not.
>
> Thanks.
>
>
> Samuel
>
>
> * 1
> *** 2
> ***** here are some keywords i like
> ******* todo
> ********* 5