floated left gallery images break blog layout

[nbachiyski]

Steps to reproduce:

1. Use a theme, which doesn't clear the floats after the post content (there are many of them)
2. Upload one photo
3. Insert [gallery] in your post
4. Save/Publish

Current: the next section, after the photo is pulled on the left of the photo, on the same line

Expected: the next section is below the photo

Here is a patch, which adds <br style="clear: both;" /> in the end of the gallery div.

[andy]

excellent, thanks Nikolay

[ryan]

(In [6801]) Fix floated left gallery layout breaks. Prop s nbachiyski. fixes #5828