Take operator precedence into account when splitting lines.

With this patch, splitting after binary operators has a panelty corresponding
to the operator's precedence. We used to ignore this and eagerly format like:

  if (aaaaaaaaaaaaaaaaaaaaaaaaa || bbbbbbbbbbbbbbbbbbbbbbbbb &&
      ccccccccccccccccccccccccc) { .. }

With this patch, this becomes:

  if (aaaaaaaaaaaaaaaaaaaaaaaaa ||
      bbbbbbbbbbbbbbbbbbbbbbbbb && ccccccccccccccccccccccccc) { .. }

llvm-svn: 171007