git diff truncation text is hard to find and offers no guidance on page

[John Chittum]

On extremely long diffs, Launchpad truncates the diff to a specific value. This value appears to be 5000 lines. However, knowing a diff is truncated, when/how it's truncated, and what to do when it's truncated is not clear

Would it be possible to have the warning about truncation moved from the bottom right, after the diff, to the top left, possibly above the download diff? And could the warning about truncation provide better guidance (when the truncation occurs, guidance to click download diff, that the truncation is _only_ in the web-ui and not the downloaded diff)?

This popped up today during a backport as there were several large changes put into our dev branch this week, and it was alarming to see that files were missing from the diff, until I scrolled all the way to the bottom and scanned outside where my eyes normally go on a review (the far right).

This appears to be an easy fix, in lib/lp/code/templates/branchmergeproposal-diff.pt moving

      <div class="boardCommentFooter"
           tal:condition="view/diff_oversized">
        The diff has been truncated for viewing.
      </div>

to below

  <div class="boardComment attachment diff">

and changing the div class to something more appropriate