Only buildable improvements are viable comparisons for determining if a city can provide a resource

Fixed techs showing "0 turns" and yet not being researched

Fixed trigger uniques with broken city filters

Added "era number", "speed modifier for stat" countables - by SomeTroglodyte 

Add buildingFilter to building maintenance unique - By PLynx01

Add Civ unique dialogue when asking for Declaration of Friendship - By ReallyBasicName

Improved AI road planning - By metablaster