seq and infinite values

[Bernhard Voelker]

As xstrold() allows 'inf' and other values, I noticed
'seq -w' does not work well with it.

[PATCH 1/2] seq: don't allow --equal-width option with infinite FIRST
[PATCH 2/2] doc: explicitly mention 'inf' values in seq(1)

Another edge case is
  seq -- -inf 0
which does endless loop while staying at "-inf".  Well, it seems
that this is mathematically correct.

BTW: xstrtold() would also allow 'NaN', but this is a more
extreme edge case for seq(1) which I don't think is
worth catching.

Have a nice day,
Berny