fixing warning for trig based chebfuns.

This is a fix for #987. So we now have:

```
>> f = chebfun(@(x) abs(x))
Warning: Function not resolved using 65537 pts. Have you tried 'splitting on'? 
> In chebfun.constructor>constructorNoSplit at 120
  In chebfun.constructor at 63
  In chebfun.chebfun>chebfun.chebfun at 221 
f =
   chebfun column (1 smooth piece)
       interval       length   endpoint values  
[      -1,       1]    65537         1        1 
Epslevel = 3.704567e-10.  Vscale = 1.
>> g = chebfun(@(x) abs(x), 'trig' )
Warning: Function not resolved using 65537 pts. Have you tried a non-trig representation? 
> In chebfun.constructor>constructorNoSplit at 120
  In chebfun.constructor at 63
  In chebfun.chebfun>chebfun.chebfun at 221 
g =
   chebfun column (1 smooth piece)
       interval       length   endpoint values trig
[      -1,       1]    65536         1        1 
Epslevel = 9.094947e-13.  Vscale = 1.
```
Closes #1318.