Document a few exceptions for the calling thread

Author: eregon

vm/boostenv/main/boostenv-decl.hh

@@ -64,6 +64,7 @@ public:
   BoostEnvironment(const VMStarter& vmStarter);
 
 // VM Management
+// All public functions may be called by any thread!
 
 public:
   inline

vm/boostenv/main/boostvm.cc

@@ -163,6 +163,7 @@ void BoostVM::run() {
   }
 }
 
+// Called by the *IO thread*
 void BoostVM::onPreemptionTimerExpire(const boost::system::error_code& error) {
   if (error != boost::asio::error::operation_aborted &&
       !_terminationRequested) {