Check that p (which is window['PIE']) exists.

Some other scripts might remove window['PIE'] mid-function-call, which would be bad and generates 'Object does not support this property or method' errors.
Should resolve issue 89.

sources/htc_init.js

@@ -2,14 +2,16 @@ var p = window['PIE'],
     el = element;
 
 function init() {
-    if( doc.media !== 'print' ) { // IE strangely attaches a second copy of the behavior to elements when printing
+    if( p && doc.media !== 'print' ) { // IE strangely attaches a second copy of the behavior to elements when printing
         p['attach']( el );
     }
 }
 
 function cleanup() {
-    p['detach']( el );
-    p = el = 0;
+    if (p) {
+        p['detach']( el );
+        p = el = 0;
+    }
 }
 
 if( el.readyState === 'complete' ) {