Remove exceeding whitespace from titles when saving.

This prevents article titles being rendered invisible in HTML
markup due to collapsing whitespace, and cleans up any
left-over bytes that likely shouldn't be there
(aka copy+paste scrap).

This scrap would otherwise also be used when constructing
the article URL. If title contains only whitespace characters,
this leads to the infamous percent encoded fallback URLs,
only consisting whitespace characters.

git-svn-id: http://textpattern.googlecode.com/svn/development/4.x@5245 2fea6a4d-a838-0410-917b-93a53c48e9d2