Support UTF-8 BOM if present.

I'm not sure if the utf-16/32 checks are the right thing to do, but as
quickbook only supports utf-8 for now, they'll work okay. Hopefully if
it ever support other encodings this should be offloaded to an
appropriate library.

[SVN r59677]

tools/quickbook

@@ -1 +1 @@
-Subproject commit baec926449cda42fe17cf9fc0c3b25b8cf3ee647
+Subproject commit ea57bed3d34fde188f3d47553abb6bd4149896ab