add a TimerGuard around db locks & ops

I moved the clocks member from LockedDatabase to Database to make this happen,
so the new DatabaseGuard (replacing a direct MutexGuard<LockedDatabase>) can
access it before acquiring the lock.

I also made the type of clock a type parameter of Database (and so several
other things throughout the system). This allowed me to drop the Arc<>, but
more importantly it means that the Clocks trait doesn't need to stay
object-safe. I plan to take advantage of that shortly.

src/cmds/config/mod.rs

@@ -125,7 +125,7 @@ struct Args {
 pub fn run() -> Result<(), Error> {
     let args: Args = super::parse_args(USAGE)?;
     let (_db_dir, conn) = super::open_conn(&args.flag_db_dir, super::OpenMode::ReadWrite)?;
-    let clocks = Arc::new(clock::RealClocks{});
+    let clocks = clock::RealClocks {};
     let db = Arc::new(db::Database::new(clocks, conn, true)?);
 
     let mut siv = Cursive::new();

src/cmds/init.rs

@@ -66,7 +66,7 @@ pub fn run() -> Result<(), Error> {
         pragma journal_mode = wal;
         pragma page_size = 16384;
     "#)?;
-    db::Database::init(&mut conn)?;
+    db::init(&mut conn)?;
     info!("Database initialized.");
     Ok(())
 }

src/cmds/run.rs

@@ -96,7 +96,7 @@ struct Syncer {
 
 pub fn run() -> Result<(), Error> {
     let args: Args = super::parse_args(USAGE)?;
-    let clocks = Arc::new(clock::RealClocks{});
+    let clocks = clock::RealClocks {};
     let (_db_dir, conn) = super::open_conn(
         &args.flag_db_dir,
         if args.flag_read_only { super::OpenMode::ReadOnly } else { super::OpenMode::ReadWrite })?;
@@ -123,7 +123,6 @@ pub fn run() -> Result<(), Error> {
         let streams = l.streams_by_id().len();
         let env = streamer::Environment {
             db: &db,
-            clocks: clocks.clone(),
             opener: &*stream::FFMPEG,
             shutdown: &shutdown_streamers,
         };