Add branch name to interim version information

This is useful for developers who may have multiple builds of the game
from various different branches and may easily forget which build of the
game is what.

This shows up in the bottom-right corner of the title screen and also
with the `-version` command-line option, and in the status message
printed when building the game.

desktop_version/src/main.cpp

@@ -401,6 +401,7 @@ int main(int argc, char *argv[])
 #ifdef INTERIM_VERSION_EXISTS
             puts(COMMIT_DATE);
             puts(INTERIM_COMMIT);
+            puts(BRANCH_NAME);
 #endif
             VVV_exit(0);
         }