CTFE Status

[Stefan Koch via Digitalmars-d]

I just fixed the "" case for StringLiterals.
However the fix is quite hackish and needs to be revisited soon.
Furthermore I have made a few more preparations for function call 
support.

The reason why I am a bit reculant to enable function calls is 
the vast increase of bug-attack-surface.

Also there has been a slight speed-increase in the interpreter 
due to the removal of stack-pointers which were a left-over from 
the time where the heap was unimplemented.

I may restore the llvm-backend temporarily to verify the 
function-call handling (one I am ready to enable it).