Fix OverflowError when loading a large term-document matrix in MatrixMarket format. Fix #1998

[arlenk]

cython mmreader was (incorrectly) assuming that num_docs, num_terms, etc. would fit in a c int.

This version uses long longs for all related types.

Related issue from @KartikTaskhuman: #1998

[menshikh-iv]

@arlenk please have a look to error - https://ci.appveyor.com/project/piskvorky/gensim-431bq/build/job/87sjiebimbr726ya#L306 (looks like a problem with python2 and L postfix for long long values)

Descriptions of reason (python2)

>>> isinstance(2, int)
True
>>> isinstance(2L, int)
False

[arlenk]

@menshikh-iv

@arlenk please have a look to error - https://ci.appveyor.com/project/piskvorky/gensim-431bq/build/job/87sjiebimbr726ya#L306 (looks like a problem with python2 and L postfix for long long values)

unfortunately I can't seem to replicate this on osx, but I think you are right, the problem is that python 2 still treats ints and longs differently. I updated the tests to use isinstance(val, numbers.Integral) instead of isinstance(val, int). It seems like most other tests were already using number.Integral instead of int already.

Hopefully this will fix the issue on the windows build.

[menshikh-iv]

Thanks for fast fix @arlenk 👍