Remove beast::Thread (RIPD-1189):

All uses of beast::Thread were previously removed from the code
base, so beast::Thread is removed.  One piece of beast::Thread
needed to be preserved: the ability to set the current thread's
name.  So there's now a beast::CurrentThreadName that allows the
current thread's name to be set and returned.

Thread naming is also cleaned up a bit.  ThreadName.h and .cpp
are removed since beast::CurrentThreadName does a better job.
ThreadEntry is also removed, but its terminateHandler() is
preserved in TerminateHandler.cpp.  The revised terminateHandler()
uses beast::CurrentThreadName to recover the name of the running
thread.

Finally, the NO_LOG_UNHANDLED_EXCEPTIONS #define is removed since
it was discovered that the MacOS debugger preserves the stack
of the original throw even if the terminateHandler() rethrows.

src/test/beast/beast_CurrentThreadName_test.cpp

@@ -0,0 +1,88 @@
+//------------------------------------------------------------------------------
+/*
+    This file is part of rippled: https://github.com/ripple/rippled
+    Copyright (c) 2017 Ripple Labs Inc.
+
+    Permission to use, copy, modify, and/or distribute this software for any
+    purpose  with  or without fee is hereby granted, provided that the above
+    copyright notice and this permission notice appear in all copies.
+
+    THE  SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
+    WITH  REGARD  TO  THIS  SOFTWARE  INCLUDING  ALL  IMPLIED  WARRANTIES  OF
+    MERCHANTABILITY  AND  FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
+    ANY  SPECIAL ,  DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+    WHATSOEVER  RESULTING  FROM  LOSS  OF USE, DATA OR PROFITS, WHETHER IN AN
+    ACTION  OF  CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
+    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+*/
+//==============================================================================
+
+#include <BeastConfig.h>
+#include <ripple/beast/core/CurrentThreadName.h>
+#include <ripple/beast/unit_test.h>
+#include <atomic>
+#include <thread>
+
+namespace ripple {
+namespace test {
+
+class CurrentThreadName_test : public beast::unit_test::suite
+{
+private:
+    static void exerciseName (
+        std::string myName, std::atomic<bool>* stop, std::atomic<int>* state)
+    {
+        // Verify that upon creation a thread has no name.
+        auto const initialThreadName = beast::getCurrentThreadName();
+
+        // Set the new name.
+        beast::setCurrentThreadName (myName);
+
+        // Indicate to caller that the name is set.
+        *state = 1;
+
+        // If there is an initial thread name then we failed.
+        if (initialThreadName)
+            return;
+
+        // Wait until all threads have their names.
+        while (! *stop);
+
+        // Make sure the thread name that we set before is still there
+        // (not overwritten by, for instance, another thread).
+        if (beast::getCurrentThreadName() == myName)
+            *state = 2;
+    }
+
+public:
+    void
+    run() override
+    {
+        // Make two different threads with two different names.  Make sure
+        // that the expected thread names are still there when the thread
+        // exits.
+        std::atomic<bool> stop {false};
+
+        std::atomic<int> stateA {0};
+        std::thread tA (exerciseName, "tA", &stop, &stateA);
+
+        std::atomic<int> stateB {0};
+        std::thread tB (exerciseName, "tB", &stop, &stateB);
+
+        // Wait until both threads have set their names.
+        while (stateA == 0 || stateB == 0);
+
+        stop = true;
+        tA.join();
+        tB.join();
+
+        // Both threads should still have the expected name when they exit.
+        BEAST_EXPECT (stateA == 2);
+        BEAST_EXPECT (stateB == 2);
+    }
+};
+
+BEAST_DEFINE_TESTSUITE(CurrentThreadName,core,beast);
+
+} // test
+} // ripple