STYLE: src/Admin: Update python scripts to use "is None" instead of "== None"

Rational copied from https://www.python.org/dev/peps/pep-0290/#testing-for-none

// -----------------
Since there is only one None object, equality can be tested with identity. Identity
tests are slightly faster than equality tests. Also, some object types may overload
comparison, so equality testing may be much slower.

Pattern:

if v == None  -->  if v is None:
if v != None  -->  if v is not None:
// -----------------

src/Admin/sitemap_gen.py

@@ -88,7 +88,7 @@ def getPage(url):
         for i in f.readlines():
             page += i
         date = f.info().getdate('Last-Modified')
-        if date == None:
+        if date is None:
             date = (0, 0, 0)
         else:
             date = date[:3]
@@ -112,7 +112,7 @@ def getRobotParser(startUrl):
     robotUrl = urlparse.urljoin(startUrl, "/robots.txt")
     page, date, url = getPage(robotUrl)
 
-    if page == None:
+    if page is None:
         print "Could not read ROBOTS.TXT at:", robotUrl
         return None
     # end if
@@ -205,11 +205,11 @@ def parsePages(startUrl, maxUrls, blockExtensions):
 
     while True:
         url = getUrlToProcess(pageMap)
-        if url == None:
+        if url is None:
             break
         print " ", url
         page, date, newUrl = getPage(url)
-        if page == None:
+        if page is None:
             del pageMap[url]
         elif url != newUrl:
             print "Redirect -> " + newUrl