api: test for RefUnwindSafe

Requiring UnwindSafe is seemingly not sufficient. We also need to
require RefUnwindSafe.

src/ahocorasick.rs

@@ -2016,11 +2016,11 @@ mod tests {
 
     #[test]
     fn oibits() {
-        use std::panic::UnwindSafe;
+        use std::panic::{RefUnwindSafe, UnwindSafe};
 
         fn assert_send<T: Send>() {}
         fn assert_sync<T: Sync>() {}
-        fn assert_unwind_safe<T: UnwindSafe>() {}
+        fn assert_unwind_safe<T: RefUnwindSafe + UnwindSafe>() {}
 
         assert_send::<AhoCorasick>();
         assert_sync::<AhoCorasick>();

src/prefilter.rs

@@ -1,12 +1,12 @@
 use std::fmt;
-use std::panic::UnwindSafe;
+use std::panic::{RefUnwindSafe, UnwindSafe};
 
 use memchr::{memchr, memchr2, memchr3};
 
 /// A prefilter describes the behavior of fast literal scanners for quickly
 /// skipping past bytes in the haystack that we know cannot possibly
 /// participate in a match.
-pub trait Prefilter: Send + Sync + UnwindSafe + fmt::Debug {
+pub trait Prefilter: Send + Sync + RefUnwindSafe + UnwindSafe + fmt::Debug {
     /// Returns the next possible match candidate. This may yield false
     /// positives, so callers must "confirm" a match starting at the position
     /// returned. This, however, must never produce false negatives. That is,