Add recovery for randomly closed socket desciptors.

Although it should never happen that a file descriptor is suddenly
closed, it appeared that this happens on linux 64bit when using
FMODex... Not really sure how useful this is, but at least now the
viewer just continues to work, as if -say- the socket was closed
remotely. Before the curl thread would go into a tight loop that it
wouldn't recover from until the watchdog thread terminated the viewer.

indra/llmessage/aicurleasyrequeststatemachine.h

@@ -81,6 +81,14 @@ class AICurlEasyRequestStateMachine : public AIStateMachine, public AICurlEasyHa
 	// Called after this curl easy handle was removed from a multi handle.
 	/*virtual*/ void removed_from_multi_handle(AICurlEasyRequest_wat&);
 
+	// Called when the curl thread detected that the socket of this handle has become unusable.
+	/*virtual*/ void bad_file_descriptor(AICurlEasyRequest_wat&);
+
+#ifdef SHOW_ASSERT
+	// Called when a command was added to remove this easy handle.
+	/*virtual*/ void queued_for_removal(AICurlEasyRequest_wat&);
+#endif
+
   protected:
 	// AIStateMachine implementations.