Listing probe alias resolution failures

[Frank Ch. Eigler]

Hi -

> [...]
> Ah, I see something I missed before with the following:
> # stap -p2 -e 'probe vm.mmap ? { printf("%p %d\n", address, length) }'
> [...]
> probe vm.mmap = kernel.function("do_mmap"), kernel.function("do_mmap2")? {
>     address = $addr
>     length = $len
> }
> [...]
> I missed the fact that the first one isn't optional.  But, shouldn't 
> making 'vm.mmap' optional basically make 'kernel.function("do_mmap")' 
> optional?

But "do_mmap" is found, and so the optional flag is satisfied.  The
probe handler is processed without further error suppression.  It's
not obvious that this is wrong. 

PS. This bug #1155 is really annoying.

- FChE