make savemessage() handle NO response to APPEND correctly

IMAP servers can return `NO` responses to the `APPEND` command,
e.g. here's an example response from Groupwise's IMAP server:

    NO APPEND The 1500 MB storage limit has been exceeded.

In this case, savemessage() should abort the repository sync rather
than returning UID 0 which would cause the local copy of the message
being saved to get irreversibly deleted.

Signed-off-by: Adam Spiers <offlineimap@adamspiers.org>
Signed-off-by: Eygene Ryabinkin <rea@codelabs.ru>

Changelog.rst

@@ -22,6 +22,9 @@ OfflineIMAP v6.5.5-rc1 (2012-09-05)
 
 * Execute pre/post-sync hooks during synchronizations
   toggled by IMAP IDLE message processing. (maxgerer@gmail.com)
+* Catch unsuccessful local mail uploads when IMAP server
+  responds with "NO" status; that resulted in a loss of such
+  local messages. (Adam Spiers)
 
 OfflineIMAP v6.5.5-rc1 (2012-09-05)
 ===================================

offlineimap/folder/IMAP.py

@@ -548,6 +548,20 @@ class IMAPFolder(BaseFolder):
                     (typ, dat) = imapobj.append(self.getfullname(),
                                        imaputil.flagsmaildir2imap(flags),
                                        date, content)
+                    # This should only catch 'NO' responses since append()
+                    # will raise an exception for 'BAD' responses:
+                    if typ != 'OK':
+                        # For example, Groupwise IMAP server can return something like:
+                        #
+                        #   NO APPEND The 1500 MB storage limit has been exceeded.
+                        #
+                        # In this case, we should immediately abort the repository sync
+                        # and continue with the next account.
+                        msg = \
+                            "Saving msg in folder '%s', repository '%s' failed (abort). " \
+                            "Server responded: %s %s\n" % \
+                            (self, self.getrepository(), typ, dat)
+                        raise OfflineImapError(msg, OfflineImapError.ERROR.REPO)
                     retry_left = 0 # Mark as success
                 except imapobj.abort as e:
                     # connection has been reset, release connection and retry.