[MERGE/RFC] Add dotted-decimal revision numbers to merge_sorted output

[Aaron Bentley]

Robert Collins wrote:
> However, at the real world level, log is not fast enough to be affected
> by this : log in a branch with 7K revisions is several orders of
> magnitude slower than 80ms.

No, when log is displaying a restricted range (e.g. -r -20..-1), it
takes ~60ms.  And it always emits a few log messages quickly, to fill
the screen.  So for log formatters that show merges, slowing down
merge_sorted could have an observable effect, because it increases the
time before the first few log messages are emitted.

It probably makes sense to run the log benchmarks before and after.

Aaron