Skip PDFs, move index.html to output directory, add --weighted option.

--weighted option had never been committed; was prototyped here before implementation in WebKit ImageDiff.

Stores index.html in the output directory rather than the current working directory.

Skips PDFs since we can't compare those.

[reed1, 2011-05-24 19:34:34]

LGTM

http://codereview.appspot.com/4557042/diff/1/tools/skdiff_main.cpp
File tools/skdiff_main.cpp (right):

http://codereview.appspot.com/4557042/diff/1/tools/skdiff_main.cpp#newcode71
tools/skdiff_main.cpp:71: static int compare_diff_weighted (DiffRecord** lhs,
DiffRecord** rhs) {
Its ok, but I find this pattern harder to see for correctness than

if lh < rh
   return -1
if lh > rh
   return 1

[TomH, 2011-06-06 14:57:26]

Committed in r1411.