hgweb: consistently add search form to all gitweb pages
Paper has it on all pages. Not sure why gitweb doesn't. I think it
should be everywhere because it is a useful feature.
Also, we weren't consistently adding the HTML in the same place. This
was OK since the element is absolutely positioned. But this bothered
me a bit, so I went ahead and fixed it.
ERROR: FIXME: This is a known failure of filelog.size for data starting with \1\n
OK.