Warnings fixes (well.. the UPnP was actually a crash fix.)

libp2p/Host.cpp

@@ -155,7 +155,7 @@ bi::tcp::endpoint Host::traverseNAT(std::vector<bi::address> const& _ifAddresses
 {
 	asserts(_listenPort != 0);
 	
-	UPnP* upnp;
+	UPnP* upnp = nullptr;
 	try
 	{
 		upnp = new UPnP;

libsolidity/Compiler.cpp

@@ -324,7 +324,7 @@ bool Compiler::visit(ExpressionStatement& _expressionStatement)
 {
 	Expression& expression = _expressionStatement.getExpression();
 	ExpressionCompiler::compileExpression(m_context, expression);
-	Type::Category category = expression.getType()->getCategory();
+//	Type::Category category = expression.getType()->getCategory();
 	for (unsigned i = 0; i < expression.getType()->getSizeOnStack(); ++i)
 		m_context << eth::Instruction::POP;
 	return false;