Fix CMake and AboutThisBuild with git (see issue #2860)

Tools to generate the release info are not updated jet, namely
tools/generateReleaseInfo{.bat}.
Only tested on Linux, OS X and Windows are untested.

rtgui/version.h.in

@@ -4,9 +4,9 @@
 #ifndef _VERSION_
 #define _VERSION_
 
-#define VERSION "${HG_VERSION}"
+#define VERSION "${GIT_VERSION}"
 #define VERSION_SUFFIX "${VERSION_SUFFIX}"
-#define TAGDISTANCE ${HG_TAGDISTANCE}
+#define TAGDISTANCE ${GIT_TAGDISTANCE}
 #define CACHEFOLDERNAME "RawTherapee${CACHE_NAME_SUFFIX}"
 
 #endif