Bug in randbn(n,p)

[aurorarossi]

The function randbn(n,p) that returns a binomially-distributed random number with parameters $n$ and $p$. For every $n$, if $p=1$ it should return $n$ instead it loops.

[aurorarossi]

Binomial.jl test is not working (but it is not included in runtests.jl). I suggest to change those tests.

[simonschoelly]

The random graphs in general is something we have to refactor at one point - form some graphs, I think we also kind of have an incorrect distribution.

In this PR: #150 I have added to the comments some code that I wrote a long time ago but never commited, that should take of the issue here. Maybe someone with a bit more time can take that old code and create a new PR out of it?