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This should greatly reduce the amount of output generated when one alias
is added/removed from a large alias group.

It also simplifies Sorted(), so that it really just sorts by pss and
doesn't put bss & padding-only symbols at the bottom. I think this is
fine for now, and if we still find that these symbols are confusing
people, we could change the diff command to explicitly print bss &
padding symbols after the main list of them (via multiple Print()
statements)

Change-Id: I23db60de6cffa6bf8a9399cb30e46cf5d92ad0f6
Reviewed-on: https://chromium-review.googlesource.com/1176167
Commit-Queue: agrieve <agrieve@chromium.org>
Reviewed-by: Samuel Huang <huangs@chromium.org>
Cr-Commit-Position: refs/heads/master@{#583491}