Error handling in comparison operators.

exceptional.scss

@@ -21,7 +21,9 @@ div[hux ~= "hello"] {
   hux: blux;
   foo: boo;
   dux: "hello" + "goodbye";
-  shux: "hello" + 12;
-  frux: 12 + "hello";
+  shux: 'hello' + 12;
+  frux: 12 + 'hello';
   blah: blah;
+  hoo: blah == 12;
+  boo: 12px >= 3em;
 }

node_comparisons.cpp

@@ -5,6 +5,7 @@
 #include <cstdlib>
 #include <cmath>
 #include "node.hpp"
+#include "error.hpp"
 
 using std::string;
 using std::stringstream;
@@ -82,11 +83,11 @@ namespace Sass {
         return numeric_value() < rhs.numeric_value();
       }
       else {
-        // TO DO: throw an exception ("units don't match")
+        throw Error(Error::evaluation, line_number, "", "incompatible units");
       }
     }
     else {
-      // TO DO: throw an exception ("incomparable types")
+      throw Error(Error::evaluation, line_number, "", "incomparable types");
     }
   }