Make sure symbolic functions return symbolic answers

[kcrisman]

From sage-support:

> I'm running Sage 4.6.2.  I've just noticed that if I evaluate various 
> symbolic expressions which return 0 then the 0 returned is a python int, 
> rather than a Sage integer.  examples of such expressions are sin(0), 
> tan(0), ln(0). 
> Is there a reason for this or is it a bug? 


I would consider this a bug, but because it should return a symbolic 
expression. 
sage: a = sin(pi) 
sage: a 
0 
sage: type(a) 
<type 'sage.symbolic.expression.Expression'> 
It's possible to get this behavior: 
sage: type(sin(0,hold=True).simplify()) 
<type 'sage.symbolic.expression.Expression'> 
Anyway, this is an oversight, I would say.  Anyone else care to 
comment?  Otherwise it would be great if you'd file a bug report. 
This is important to fix, because some Sage code depends on the input 
in integer form being Sage integer or something else with Sage 
methods, not a Python int, and one could imagine someone relying on 
this and getting a nasty exception. 

[burcin]

This is a duplicate of #10133.