Fix clippy::significant_drop_in_scrutinee warnings

This is apparently a new warning from clippy nightly, documented in
https://rust-lang.github.io/rust-clippy/master/index.html#significant_drop_in_scrutinee .

I'm not in love with the temporary variables that this warning wants
me to introduce, but it does seem like a decent way to avoid some
kinds of deadlock.

crates/tor-dirmgr/src/lib.rs

@@ -376,11 +376,14 @@ impl<R: Runtime> DirMgr<R> {
             v.store(false, Ordering::SeqCst);
         });
 
-        let schedule = match self.task_schedule.lock().expect("poisoned lock").take() {
-            Some(sched) => sched,
-            None => {
-                debug!("Attempted to bootstrap twice; ignoring.");
-                return Ok(());
+        let schedule = {
+            let sched = self.task_schedule.lock().expect("poisoned lock").take();
+            match sched {
+                Some(sched) => sched,
+                None => {
+                    debug!("Attempted to bootstrap twice; ignoring.");
+                    return Ok(());
+                }
             }
         };
 

crates/tor-dirmgr/src/shared_ref.rs

@@ -79,12 +79,12 @@ impl<T> SharedMutArc<T> {
         F: FnOnce(&mut T) -> Result<U>,
         T: Clone,
     {
-        match self
+        let mut writeable = self
             .dir
             .write()
-            .expect("Poisoned lock for directory reference")
-            .as_mut()
-        {
+            .expect("Poisoned lock for directory reference");
+        let dir = writeable.as_mut();
+        match dir {
             None => Err(Error::DirectoryNotPresent), // Kinda bogus.
             Some(arc) => func(Arc::make_mut(arc)),
         }

crates/tor-guardmgr/src/lib.rs

@@ -591,8 +591,8 @@ impl<R: Runtime> GuardMgr<R> {
     ) {
         let now = self.runtime.now();
         let mut inner = self.inner.lock().expect("Poisoned lock");
-
-        for id in inner.lookup_ids(ed_identity, rsa_identity) {
+        let ids = inner.lookup_ids(ed_identity, rsa_identity);
+        for id in ids {
             match &id.0 {
                 FirstHopIdInner::Guard(id) => {
                     inner.guards.active_guards_mut().record_failure(

crates/tor-persist/src/testing.rs

@@ -96,7 +96,8 @@ impl StateMgr for TestingStateMgr {
     {
         let inner = self.inner.lock().expect("Lock poisoned.");
         let storage = inner.storage.lock().expect("Lock poisoned.");
-        match storage.entries.get(key) {
+        let content = storage.entries.get(key);
+        match content {
             Some(value) => Ok(Some(serde_json::from_str(value).map_err(load_error)?)),
             None => Ok(None),
         }