Press This sideloader fixes and wp_handle_upload fixes

[noel]

Press This was not sideloading images as it was intended. This was actually a good feature to leave out as I found a bug in the wp_upload_dir function that would allow the $url to be == to the $dir and output something ugly like:

​http://bookmarklet.site//Users/noel/Sites/bookmarklet.site/public/wp-content/uploads/2008/07/filename.jpg

Fixes are short and sweet.

[noel]

Press This and patches for wp_upload_dir()

[ryan]

(In [8369]) Image sideload and wp_upload_dir() fixes from noel. fixes #7342 for trunk

[ryan]

(In [8370]) Image sideload and wp_upload_dir() fixes from noel. fixes #7342 for 2.6