Unable to read csv file with uneven rows

https://archive.ics.uci.edu/ml/machine-learning-databases/plants/plants.data

```
>>> dt.fread("~/Downloads/plants.data.txt")
Traceback (most recent call last):
File "", line 1, in
File "/Users/pasha/py36/lib/python3.6/site-packages/typesentry/config.py", line 155, in fdecorated
ret = f(*args, **kws)
File "/Users/pasha/github/datatable/datatable/fread.py", line 69, in fread
return freader.read()
File "/Users/pasha/github/datatable/datatable/fread.py", line 301, in read
_dt = c.fread(self)
RuntimeError: Line 2 has too few fields when detecting types. Use fill=TRUE to pad with NA. Expecting 2 fields but found 1: "abies,ak,az,ca,co,ct,ga,id,in,ia,me,md,ma,mi,mn,mt,nv,nh,nm,ny,nc,oh,or,pa,ri,tn,ut,vt,va,wa,wv,wi,wy,ab,bc,lb,mb,nb,nf,nt,ns,nu,on,pe,qc,sk,yt,fraspm"

>>> dt.fread("~/Downloads/plants.data.txt", fill=True)
Traceback (most recent call last):
File "", line 1, in
File "/Users/pasha/py36/lib/python3.6/site-packages/typesentry/config.py", line 155, in fdecorated
ret = f(*args, **kws)
File "/Users/pasha/github/datatable/datatable/fread.py", line 69, in fread
return freader.read()
File "/Users/pasha/github/datatable/datatable/fread.py", line 301, in read
_dt = c.fread(self)
RuntimeError: Could not find first good line start after jump point 1 when sampling.
```