Fix JET errors around matching methods for send_msg_now(...) (#165)

```
┌  @ Distributed /workpath/Distributed.jl/src/process_messages.jl:321
│ no matching method found `send_msg_now(::Distributed.LocalProcess, ::Distributed.MsgHeader, ::Distributed.IdentifySocketAckMsg)` (1/2 union split): Distributed.send_msg_now(w, Distributed.MsgHeader()::Distributed.MsgHeader, Distributed.IdentifySocketAckMsg()::Distributed.IdentifySocketAckMsg)
└────────────────────
```

```
┌  @ Distributed /workpath/Distributed.jl/src/process_messages.jl:359
│ no matching method found `send_msg_now(::Distributed.LocalProcess, ::Distributed.MsgHeader, ::Distributed.JoinCompleteMsg)` (1/2 union split): Distributed.send_msg_now(controller::Union{Distributed.LocalProcess, Distributed.Worker}, Distributed.MsgHeader(Distributed.RRID(0, 0)::Distributed.RRID, (header::Distributed.MsgHeader).notify_oid::Distributed.RRID)::Distributed.MsgHeader, Distributed.JoinCompleteMsg((Distributed.Sys).CPU_THREADS::Int64, Distributed.getpid()::Int32)::Distributed.JoinCompleteMsg)
└────────────────────
```

```
┌ connect_to_peer(manager::Distributed.ClusterManager, rpid::Int64, wconfig::Distributed.WorkerConfig) @ Distributed /workpath/Distributed.jl/src/process_messages.jl:368
│ no matching method found `send_msg_now(::Distributed.LocalProcess, ::Distributed.MsgHeader, ::Distributed.IdentifySocketMsg)` (1/2 union split): Distributed.send_msg_now(w, Distributed.MsgHeader()::Distributed.MsgHeader, Distributed.IdentifySocketMsg(myid()::Int64)::Distributed.IdentifySocketMsg)
└────────────────────
```

```
┌ send_msg_now(s::Base.PipeEndpoint, header::Distributed.MsgHeader, msg::Distributed.ResultMsg) @ Distributed //workl/clones/JuliaLang/Distributed.jl/src/messages.jl:113
│ no matching method found `send_msg_now(::Distributed.LocalProcess, ::Distributed.MsgHeader, ::Distributed.(1/2 union split): Distributed.send_msg_now(Distributed.worker_from_id(id::Int64)::Union{Distributed.LocalProcess, Worker}, header::Distributed.MsgHeader, msg::Distributed.ResultMsg)
└────────────────────
```

(cherry picked from commit 305d6fc4280de14f015c13a080c785bf68c34785)
(cherry picked from commit 871e3d746ab0c7668462f7b88515a362da9c11f1)

Author: DilumAluthge

src/messages.jl

@@ -110,7 +110,7 @@ end
 function send_msg_now(s::IO, header, msg::AbstractMsg)
     id = worker_id_from_socket(s)
     if id > -1
-        return send_msg_now(worker_from_id(id), header, msg)
+        return send_msg_now(worker_from_id(id)::Worker, header, msg)
     end
     send_msg_unknown(s, header, msg)
 end

src/process_messages.jl

@@ -316,7 +316,7 @@ end
 
 function handle_msg(msg::IdentifySocketMsg, header, r_stream, w_stream, version)
     # register a new peer worker connection
-    w = Worker(msg.from_pid, r_stream, w_stream, cluster_manager; version=version)
+    w = Worker(msg.from_pid, r_stream, w_stream, cluster_manager; version=version)::Worker
     send_connection_hdr(w, false)
     send_msg_now(w, MsgHeader(), IdentifySocketAckMsg())
     notify(w.initialized)
@@ -329,7 +329,7 @@ end
 
 function handle_msg(msg::JoinPGRPMsg, header, r_stream, w_stream, version)
     LPROC.id = msg.self_pid
-    controller = Worker(1, r_stream, w_stream, cluster_manager; version=version)
+    controller = Worker(1, r_stream, w_stream, cluster_manager; version=version)::Worker
     notify(controller.initialized)
     register_worker(LPROC)
     topology(msg.topology)
@@ -362,7 +362,7 @@ end
 function connect_to_peer(manager::ClusterManager, rpid::Int, wconfig::WorkerConfig)
     try
         (r_s, w_s) = connect(manager, rpid, wconfig)
-        w = Worker(rpid, r_s, w_s, manager; config=wconfig)
+        w = Worker(rpid, r_s, w_s, manager; config=wconfig)::Worker
         process_messages(w.r_stream, w.w_stream, false)
         send_connection_hdr(w, true)
         send_msg_now(w, MsgHeader(), IdentifySocketMsg(myid()))