Require one or more spaces (+) between keyword and headline

Require one or more spaces (+) between keyword and headline

* org.el (org-scan-tags): Require one or more spaces (+) between
keyword and headline.

Otherwise the re will match a line like:

* TODO@ Foobar

And assumes the @ to be part of the headline.

This fixes a glitch reported by Simon Thum in
<4F53DEF7.8080604@gmx.de>.

> Hi all,
>
> I have found some irritating behaviour, potentially a bug. I have a
> block agenda which goes like:
>
> tags-todo "@home&TODO=\"TODO\"
>
> and it displays a certain org line that reads
>
> **** TODO_ state triggers
>
> Which is just a heading for dealing with TODO state triggers, and I
> appended the _ as I don't want it to be a TODO.
>
> For example, the global TODO list and syntax highlighting does not
> consider it a todo, but C-c a m TODO="TODO" does. TODO="T" does not,
> so it's not very grave.
>
> Most likely, it's simply an inconsistency arising from not having a
> real parser. I just wanted to report it here so it may get fixed.