Catch more exceptions in dtors

Misc coverity reports

src/common/threadpool.cpp

@@ -51,11 +51,19 @@ threadpool::threadpool(unsigned int max_threads) : running(true), active(0) {
 }
 
 threadpool::~threadpool() {
+  try
   {
     const boost::unique_lock<boost::mutex> lock(mutex);
     running = false;
     has_work.notify_all();
   }
+  catch (...)
+  {
+    // if the lock throws, we're just do it without a lock and hope,
+    // since the alternative is terminate
+    running = false;
+    has_work.notify_all();
+  }
   for (size_t i = 0; i<threads.size(); i++) {
     try { threads[i].join(); }
     catch (...) { /* ignore */ }
@@ -91,11 +99,13 @@ unsigned int threadpool::get_max_concurrency() const {
 
 threadpool::waiter::~waiter()
 {
+  try
   {
     boost::unique_lock<boost::mutex> lock(mt);
     if (num)
       MERROR("wait should have been called before waiter dtor - waiting now");
   }
+  catch (...) { /* ignore */ }
   try
   {
     wait(NULL);