Add call to compute diffs via local PHP server

This is inefficient as it requires an individal request per diff.

Going to try collecting the revision texts to reduce communication
overhead.

Signed-off-by: Will Beason <willbeason@gmail.com>

test/Wikiq_Unit_Test.py

@@ -107,6 +107,7 @@ class WikiqTestCase(unittest.TestCase):
 
         try:
             tester.call_wikiq()
+            # tester.call_wikiq("--compute-incremental-diffs")
         except subprocess.CalledProcessError as exc:
             self.fail(exc.stderr.decode("utf8"))