Do not use potentially not unique id to collapse

generated html can be added many time in one page relying on line number
to collapse is dangerous.

Walking the dom to  get next children is more reliable

Cython/Compiler/Annotate.py

@@ -66,11 +66,11 @@ class AnnotationCCodeWriter(CCodeWriter):
         return css
 
     _js = """
-function toggleDiv(id) {
-    theDiv = document.getElementById(id);
+    function toggleDiv(id) {
+        theDiv = id.nextElementSibling
         if (theDiv.style.display != 'block') theDiv.style.display = 'block';
         else theDiv.style.display = 'none';
-}
+    }
     """
 
 
@@ -99,7 +99,7 @@ body { font-family: courier; font-size: 12; }
 
 .cython.line { margin: 0em }
 
-    """
+"""
 
     def save_annotation(self, source_filename, target_filename):
         with closing(Utils.open_source_file(source_filename)) as f:
@@ -192,7 +192,7 @@ body { font-family: courier; font-size: 12; }
             score = (5 * calls['py_c_api'] + 2 * calls['pyx_c_api'] +
                      calls['py_macro_api'] + calls['pyx_macro_api'])
             #color = u"FFFF%02x" % int(255/(1+score/10.0))
-            outlist.append(u"<pre class='cython line score-%s' onclick='toggleDiv(\"line%s\")'>" % (score, k))
+            outlist.append(u"<pre class='cython line score-%s' onclick='toggleDiv(this)'>" % (score))
 
             outlist.append(u" %d: " % k)
             for c, cc, html in special_chars:
@@ -200,7 +200,7 @@ body { font-family: courier; font-size: 12; }
             outlist.append(line.rstrip())
 
             outlist.append(u'</pre>\n')
-            outlist.append(u"<pre id='line%s' class='cython code score-%s' >%s</pre>" % (k, score, code))
+            outlist.append(u"<pre class='cython code score-%s' >%s</pre>" % (score, code))
         return outlist
 
 _parse_code = re.compile(