Add clock_timebase(), clock_set_timebase().

src/sclock.c

@@ -124,6 +124,15 @@ double clock_speed( SClock *clk ) {
     return clk ? clk->speed : 0;
 }
 
+void clock_set_timebase( SClock *clk, double timebase ) {
+    if(clk)
+	clk->basetime = timebase;
+}
+
+double clock_timebase( SClock *clk ) {
+    return clk ? clk->basetime : 0;
+}
+
 void clock_set_step( SClock *clk, double step ) {
     if(clk) clk->deltatime = step;
 }