Rename .sig to .selector on function types

libsolidity/ast/Types.cpp

@@ -2438,7 +2438,7 @@ MemberList::MemberMap FunctionType::nativeMembers(ContractDefinition const*) con
 		MemberList::MemberMap members;
 		if (m_kind == Kind::External)
 			members.push_back(MemberList::Member(
-				"sig",
+				"selector",
 				make_shared<FixedBytesType>(4)
 			));
 		if (m_kind != Kind::BareDelegateCall && m_kind != Kind::DelegateCall)

libsolidity/codegen/ExpressionCompiler.cpp

@@ -1068,7 +1068,7 @@ bool ExpressionCompiler::visit(MemberAccess const& _memberAccess)
 			solAssert(false, "Invalid member access to integer");
 		break;
 	case Type::Category::Function:
-		if (member == "sig")
+		if (member == "selector")
 		{
 			m_context << Instruction::SWAP1 << Instruction::POP;
 			/// need to store store it as bytes4