- Change runtime standalone detection:

* com_standalone now read-only
  * add new cvars com_basegame, com_homepath
  * standalone now automatically detected when com_basegame is set to something different than baseq3 and no id pak pk3s are found
  * This fixes https://bugzilla.icculus.org/show_bug.cgi?id=4699
- Replace a few hardcoded string literals with macros
- Add checks for Team Arena PK3s to FS_CheckPak0()

code/qcommon/q_shared.h

@@ -36,6 +36,7 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 #else
   #define PRODUCT_NAME			"ioq3"
   #define BASEGAME			"baseq3"
+  #define BASETA			"missionpack"
   #define CLIENT_WINDOW_TITLE     	"ioquake3"
   #define CLIENT_WINDOW_MIN_TITLE 	"ioq3"
   #define GAMENAME_FOR_MASTER		"Quake3Arena"