DHAT: when the run ends, print a how-to-view-the-profile hint message. n-i-bz.

DHAT: when the run ends, print a how-to-view-the-profile hint message.  n-i-bz.

The aim is to make it zero-effort for users to view the profile after
a run.  The printed message is as follows:

  To view the resulting profile, open
    file:///path/to/valgrind/installation/lib/valgrind/dh_view.html
  in a web browser, click on "Load..." and then select the file
    /path/to/dhat.out.12345
  Scroll to the end the displayed page to see a short
  explanation of some of the abbreviations used in the page.

This patch adds printing of the message, then filters it out in
dhat/tests/filter_stderr, and updates the .stderr.exp files to
remove blank lines.