Specify fixed number of columns in parser, break if mismatch
cf #2430 

```
I'm still having problems with this:

data = ('a:b\n'
'c:d:e\n'
'f:g:h:i\n'
'j:k\n'
'ln\n')

##if first row does not match longest line length, you error out doing this
print pandas.read_csv(StringIO(data),header=None,sep=':')
##even if u specify names..
print pandas.read_csv(StringIO(data),header=None,sep=':',names=list(np.arange(4)))

It would be really awesome if there was a way to force the parser to expect a fixed number of columns.
```
