Regenerate build stuff with Automake 1.13.4.

Up from Automake 1.13.3, which was released earlier in June 2013.
Man, there have been a lot of Automake releases lately.
Check for `clang-format' at configure time.

clang-format is a run-time dependency.  As such, we print a warning if
we can't find it at configure time, but we don't fail at configure time
if it is not found.
Update copyright years.