Skip printing the backtrace for RecvError/SendError

We currently get tons of useless backtraces clogging up the output when we have a panic cascade. This adds a handler that outputs a single line when a thread panics due to a sender or receiver hanging up, since this is almost always due to a panic cascade.

components/util/lib.rs

@@ -9,6 +9,7 @@
 #![cfg_attr(feature = "non-geckolib", feature(decode_utf16))]
 #![feature(optin_builtin_traits)]
 #![feature(plugin)]
+#![feature(panic_handler)]
 #![feature(reflect_marker)]
 #![feature(step_by)]