Clock test improved to allow for a +/-1% variation in cycles.

test/unit.src.common.clock.spec.js

   });
 
   it("4Khz for approx. 1 second", function(){
-    let dt = speedTest(4000); 
-    expect(count).to.be.lt(4004);
+    let ts = 4000;
+    let d = ts * 0.01;
+    let dt = speedTest(ts); 
+    expect(count).to.be.gt(ts - d);
+    expect(count).to.be.lt(ts + d);
     expect(dt).to.be.lt(1000);
   });
 
   it("4Mhz for approx. 1 second", function(){
-    let dt = speedTest(4000000); 
-    expect(count).to.be.lt(4000004);
+    let ts = 4000000;
+    let d = ts * 0.01;
+    let dt = speedTest(ts); 
+    expect(count).to.be.gt(ts - d);
+    expect(count).to.be.lt(ts + d);
     expect(dt).to.be.lt(1000);
   });
 });