Switch implementation

[bearophile]

bioinfornatics:

> with ldc and tango (up to date)
> $ ldc -O5 -release -enable-inlining test.d
> $ time ./test
> 1500000 1300000 497200000
> 
> real	0m4.376s
> user	0m4.373s
> sys	0m0.001s

LDC has llvm back-end, that doesn't share that dmd problem.
But to give us meaningful data, I suggest you to time the C program too on your machine, so we can compare :-)

Bye,
bearophile