Make live event backup files savedata specific (new format: `live%s.bkp`, where %s is the time attack folder name/savegame name - so vanilla's is `livesrb2sav.bkp`).

src/d_main.c

@@ -1135,7 +1135,7 @@ void D_SRB2Main(void)
 
 	// default savegame
 	strcpy(savegamename, SAVEGAMENAME"%u.ssg");
-	strcpy(liveeventbackup,"liveevent.bkp"); // intentionally not ending with .ssg
+	strcpy(liveeventbackup, "live"SAVEGAMENAME".bkp"); // intentionally not ending with .ssg
 
 	{
 		const char *userhome = D_Home(); //Alam: path to home

src/dehacked.c

@@ -4211,6 +4211,9 @@ static void readmaincfg(MYFILE *f)
 				// can't use sprintf since there is %u in savegamename
 				strcatbf(savegamename, srb2home, PATHSEP);
 
+				strcpy(liveeventbackup, va("live%s.bkp", timeattackfolder));
+				strcatbf(liveeventbackup, srb2home, PATHSEP);
+
 				gamedataadded = true;
 				titlechanged = true;
 			}