better YMU759 support

time base now loaded as rate and timer no longer bugs out

also you can save YMU759 songs as .fur now, even if it is pointless

src/engine/engine.cpp

@@ -506,6 +506,34 @@ bool DivEngine::loadDMF(unsigned char* file, size_t len) {
       ds.arpLen=1;
     }
 
+    if (ds.system[0]==DIV_SYSTEM_YMU759) {
+      switch (ds.timeBase) {
+        case 0:
+          ds.hz=248;
+          break;
+        case 1:
+          ds.hz=200;
+          break;
+        case 2:
+          ds.hz=100;
+          break;
+        case 3:
+          ds.hz=50;
+          break;
+        case 4:
+          ds.hz=25;
+          break;
+        case 5:
+          ds.hz=20;
+          break;
+        default:
+          ds.hz=248;
+          break;
+      }
+      ds.customTempo=true;
+      ds.timeBase=0;
+    }
+
     logI("reading pattern matrix (%d)...\n",ds.ordersLen);
     for (int i=0; i<getChannelCount(ds.system[0]); i++) {
       for (int j=0; j<ds.ordersLen; j++) {
@@ -1344,13 +1372,6 @@ SafeWriter* DivEngine::saveFur() {
   std::vector<int> patPtr;
   size_t ptrSeek;
 
-  // fail if this is an YMU759 song
-  if (song.system[0]==DIV_SYSTEM_YMU759) {
-    logE("cannot save YMU759 song!\n");
-    lastError="YMU759 song saving is not supported";
-    return NULL;
-  }
-
   SafeWriter* w=new SafeWriter;
   w->init();
   /// HEADER

src/engine/playback.cpp

@@ -643,15 +643,6 @@ void DivEngine::nextRow() {
     }
   }
 
-  if (song.system[0]==DIV_SYSTEM_YMU759) {
-    if (speedAB) {
-      ticks=speed2;
-      nextSpeed=speed1;
-    } else {
-      ticks=speed1;
-      nextSpeed=speed2;
-    }
-  } else {
   if (speedAB) {
     ticks=speed2*(song.timeBase+1);
     nextSpeed=speed1;
@@ -659,7 +650,6 @@ void DivEngine::nextRow() {
     ticks=speed1*(song.timeBase+1);
     nextSpeed=speed2;
   }
-  }
   speedAB=!speedAB;
 
   // post row details
@@ -679,31 +669,7 @@ bool DivEngine::nextTick(bool noAccum) {
   if (song.customTempo) {
     divider=song.hz;
   } else {
-    if (song.system[0]==DIV_SYSTEM_YMU759) {
+    if (song.pal) {
-      switch (song.timeBase) {
-        case 0:
-          divider=248;
-          break;
-        case 1:
-          divider=210;
-          break;
-        case 2:
-          divider=100;
-          break;
-        case 3:
-          divider=50;
-          break;
-        case 4:
-          divider=25;
-          break;
-        case 5:
-          divider=20;
-          break;
-        default:
-          divider=248;
-          break;
-      }
-    } else if (song.pal) {
       divider=60;
     } else {
       divider=50;