revset: raise ValueError when calling min or max on empty smartset
min([]) raise a ValueError, we do the same thing in smartset.min() and
smartset.max() for the sake of consistency.
The min/amax test are greatly improved in the process to prevent this familly
of regression
$ hg init
$ echo a > a
$ hg add a
$ hg commit -m test
Do we ever miss a sub-second change?:
$ for i in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20; do
> hg co -qC 0
> echo b > a
> hg st
> done
M a
M a
M a
M a
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M a
M a
M a
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M a
M a
M a
M a
M a
M a
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M a
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M a