We want inputs for function names to follow SE-0021 with the exception
that a function with no arguments is spelled `foo()` instead of `foo`,
because we have no type to disambiguate with and it's not ambiguous with
a call in this context.
Internally, we use a filter name without underscores because we don't
want to introduce spurious matches to the `_` character which might be
part of identifiers.
For now, continue to accept the old names to ease the transition.
rdar://problem/24350800
c77af6907e