- Fix potential out-of-bounds read in files.c, fix by using new FS_IsExt

- Add capability to load demos with com_protocol suffix, partially applied patches from Simon McVittie
- Fix demo loading if protocol number has more digits than 2
- Minor refactoring, replace all occurances of suffix "dm_" with global macro DEMOEXT

code/qcommon/q_shared.h

@@ -55,6 +55,8 @@ Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
 #define MAX_TEAMNAME		32
 #define MAX_MASTER_SERVERS      5	// number of supported master servers
 
+#define DEMOEXT	"dm_"			// standard demo extension
+
 #ifdef _MSC_VER
 
 #pragma warning(disable : 4018)     // signed/unsigned mismatch