Temporary: Recipient: remove remaining_capacity(), implement send_if_…

…not_full() differently

I expect that at least the second point will be resolved (more correctly) by #20.

Not sure whether we want to keep Recipient::remaining_capacity() or whether
it will be eventually superseded by #22.

This a temporary commit just to make prototyping of #11 easier.

src/lib.rs

@@ -671,22 +671,16 @@ impl<M> Recipient<M> {
     /// frequently full (slow consumer), but would still like to be notified if a
     /// different error occurs (e.g. disconnection).
     pub fn send_if_not_full<N: Into<M>>(&self, message: N) -> Result<(), SendError> {
-        if self.remaining_capacity().unwrap_or(usize::max_value()) > 1 {
-            return self.send(message);
-        }
-
-        Ok(())
+        self.try_send(message).or_else(|err| match err {
+            SendError::Full => Ok(()),
+            other => Err(other),
+        })
     }
 
     pub fn stop(&self) -> Result<(), SendError> {
         self.control_tx.send(Control::Stop).map_err(|_| SendError::Disconnected)
     }
 
-    // TODO(ryo): Properly support the concept of priority channels.
-    pub fn remaining_capacity(&self) -> Option<usize> {
-        self.message_tx.capacity().map(|capacity| capacity - self.message_tx.len())
-    }
-
     pub fn control_addr(&self) -> ControlAddr {
         ControlAddr { control_tx: self.control_tx.clone() }
     }