Support switch complexity

[richierocks]

I expected this to return 6, but I get 1:

cyclocomp(quote(switch("e", a = 1, b = 2, c = 3, d = 4, e = 5, 6)))

I think calls to switch ought to return the number of non-missing elements of ....

In this example, a and b resolve to the same thing, so there are only 2 paths through the code:

switch("a", a = , b = 2, c = 3)

[gaborcsardi]

Thanks, that's definitely a good idea.

In general, we cannot really detect if a function is computing on the language and then conditionally executes code, but at least we can handle the built-in ones.