Improved homog-test.js' mutation score to 0.8

Mutation analysis was performed on homog-test.js with Mutator (http://ortask.com/mutator/). I improved the test suite's mutation score from 0.63 to 0.8. 

In order to get to raise the quality of the test suite to 1.0, the following issue needs to be resolved: rockbot#22

Author: omgm

tests/homog-test.js

@@ -6,6 +6,12 @@ var should = require('should');
 var Matrix = require('../').matrix;
 
 describe('Create a homogenous matrix', function () {
+  it('detects bad rotation matrix', function () {
+    var Rz = new Matrix(3, 4);
+    (function () {
+      var H1 = new Homog(Rz, 0);
+    }).should.throw();
+  });
   it('rotating about the z-axis by pi/2 radians', function () {
     var Rz = new Rotate.RotZ(Math.PI/2);
     var H1 = new Homog(Rz, 0);