[with patch] IntegerVectors_nk

[malb]

calling IntegerVectors?.list after applying the attached patch is much faster now.

old:

sage: time l1 = map(tuple, IntegerVectors(2, 60).list())
CPU time: 5.01 s,  Wall time: 5.11 s

new:

sage: time l1 = map(tuple, IntegerVectors(2, 60).list())
CPU time: 0.20 s,  Wall time: 0.20 s

[mhansen]

Updated patch attached.

[malb]

Please note that the cleaner version by mhansen is by a factor of three than the original submission:

the untouched implementation
sage: time l1 = map(tuple, IntegerVectors(2, 60).list())
CPU times: user 5.06 s, sys: 0.11 s, total: 5.18 s
Wall time: 5.18

mhansen's implementation

sage: time l1 = map(tuple, IntegerVectors(2, 60, min_part=0).list())
CPU time: 0.56 s,  Wall time: 0.57 s

malb's original submission

sage: time l1 = map(tuple, IntegerVectors(2, 60).list())
CPU time: 0.20 s,  Wall time: 0.20 s

I don't mean to push my original patch (which's problems were fixed by mhansen) but propose to optimise mhansen's patch eventually.

[mabshoff]

applied mhansen's patch to 2.8.12.rc0