[z2085] Improve support for game/ subdirectories

* Add game directory to AdditionalIncludes (VC90)
* Add game directory to AdditionalIncludes (VC100)
* Simplify #include macros for subdirectories

Thanks to Shyax, LordJZ and Zergtmn for testing cmake

(based on commit [12124] - f363c78)

(based on commit [s1703] - e3317a8)