OK, just for the non-coders, like me: the mentioned file has a line, similar to #define OPENXCOM_VERSION_SHORT "1.0"
That can be adjusted. Just for housekeeping of the version, one can enter the desired string, e. g. "Nightly 1.0 2015-05-04-18-46". This is shown in the main menu. The other strings can also be seen, in that short moment during start-command and main menu. Usually it's the easiest way, to change the short-parameter, as it will be seen the easiest way.