Allow "deprecated" to accept more than string literals while parsing

[Daniel Murphy via Digitalmars-d]

"Dicebot"  wrote in message news:odfsgqcftykjkztsgqmc at forum.dlang.org...

> Is there any reason to not allow argument to be any expression and reject 
> non-string ones at semantic phase?

The original reason is that trying to reference manifest constants etc from 
that context resulted in forward reference errors, so allowing only string 
literals was easier.  I'm guessing those problems have since been fixed, so 
allowing any ct expression that resolves to a string should be fine now.