fix bug in emit-cpp for the case where we need to include BOTH <vector> and <string>
fix bug in emit-cpp for the case where we need to include BOTH <vector> and <string>

lcm-proj/lcm,andybarry/lcm,vooon/lcm-vala,adeschamps/lcm,kyonifer/lcm,DougFirErickson/lcm,kyonifer/lcm,adeschamps/lcm,andybarry/lcm,bluesquall/lcm,DougFirErickson/lcm,bluesquall/lcm,bluesquall/lcm,vooon/lcm-vala,DougFirErickson/lcm,adeschamps/lcm,DougFirErickson/lcm,DougFirErickson/lcm,kyonifer/lcm,kyonifer/lcm,lcm-proj/lcm,vooon/lcm-vala,DougFirErickson/lcm,andybarry/lcm,kyonifer/lcm,andybarry/lcm,adeschamps/lcm,vooon/lcm-vala,bluesquall/lcm,andybarry/lcm,vooon/lcm-vala,lcm-proj/lcm,bluesquall/lcm,vooon/lcm-vala,adeschamps/lcm,andybarry/lcm,vooon/lcm-vala,vooon/lcm-vala,adeschamps/lcm,adeschamps/lcm,andybarry/lcm,lcm-proj/lcm,DougFirErickson/lcm,lcm-proj/lcm,DougFirErickson/lcm,lcm-proj/lcm,kyonifer/lcm,lcm-proj/lcm,kyonifer/lcm,lcm-proj/lcm,bluesquall/lcm,bluesquall/lcm,adeschamps/lcm,andybarry/lcm