text: Title: Gensim's FastText model reads in unsupported modes from Facebook's FastText
  Body: In gensim/models/fasttext.py:
  
  ```python
      model = FastText(
          vector_size=m.dim,
          vector_size=m.dim,
          window=m.ws,
          window=m.ws,
          epochs=m.epoch,
          epochs=m.epoch,
          negative=m.neg,
          negative=m.neg,
          # FIXME: these next 2 lines read in unsupported FB FT modes (loss=3 softmax or loss=4 onevsall,
          # or model=3 supervised) possibly creating inconsistent gensim model likely to fail later. Displaying
          # clear error/warning with explanatory message would be far better - even if there might be some reason
          # to continue with the load - such as providing read-only access to word-vectors trained those ways. (See:
          # https://github.com/facebookresearch/fastText/blob/2cc7f54ac034ae320a9af784b8145c50cc68965c/src/args.h#L19
          # for FB FT mode definitions.)
          hs=int(m.loss == 1),
          hs=int(m.loss == 1),
          sg=int(m.model == 2),
          sg=int(m.model == 2),
          bucket=m.bucket,
          bucket=m.bucket,
          min_count=m.min_count,
          min_count=m.min_count,
          sample=m.t,
          sample=m.t,
          min_n=m.minn,
          min_n=m.minn,
          max_n=m.maxn,
          max_n=m.maxn,
      )
  ```