Use sa_unwrap in isbg

`isbg.py` now tries to import and use `sa_unwrap.py` to unwrap mails that
are SA reports with the original spam mail embedded.

This only works if the `isbg` module is loaded properly. To stay
compatible with users calling `isbg.py` directly, `unwrap` is replaced
by a dummy no-op function if imprting `sa_unwrap` fails.

isbg/isbg.py

@@ -65,6 +65,13 @@
 
 import sys  # Because sys.stderr.write() is called bellow
 
+try:
+    from isbg.sa_unwrap import unwrap
+except ImportError:
+    sys.stderr.write('Cannot load sa_unwrap, please install isbg package properly!')
+    # Create No-Op dummy function
+    unwrap = lambda x: None
+
 try:
     from docopt import docopt  # Creating command-line interface
 except ImportError:
@@ -421,6 +428,10 @@ def spamassassin(self):
         for u in uids:
             # Retrieve the entire message
             body = self.getmessage(u, self.pastuids)
+            # Unwrap spamassassin reports
+            unwrapped = unwrap(body)
+            if unwrapped is not None:
+                body = unwrapped
 
             # Feed it to SpamAssassin in test mode
             if self.dryrun:
@@ -569,6 +580,10 @@ def spamlearn(self):
 
                 for u in uids:
                     body = self.getmessage(u)
+                    # Unwrap spamassassin reports
+                    unwrapped = unwrap(body)
+                    if unwrapped is not None:
+                        body = unwrapped
                     if self.dryrun:
                         out = self.alreadylearnt
                         code = 0