Implement clean CTRL-C termination

Previously, we would simply bail out in an ugly way, potentially leaving
temporary files around etc, or while writing status files. Hand SIGINT
and SIGTERM as an event to the Account class, and make that bail out
cleanly at predefined points. Stopping on ctrl-c can take a few seconds
(it will e.g. finish to transfer the ongoing message), but it will shut
down cleanly.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>

offlineimap/folder/Base.py

@@ -18,6 +18,7 @@
 from offlineimap import threadutil
 from offlineimap.ui import getglobalui
 from offlineimap.error import OfflineImapError
+import offlineimap.accounts
 import os.path
 import re
 from sys import exc_info
@@ -332,6 +333,9 @@ class BaseFolder(object):
                             self.getmessageuidlist())
         num_to_copy = len(copylist)
         for num, uid in enumerate(copylist):
+            # bail out on CTRL-C or SIGTERM
+            if offlineimap.accounts.Account.abort_NOW_signal.is_set():
+                break
             self.ui.copyingmessage(uid, num+1, num_to_copy, self, dstfolder)
             # exceptions are caught in copymessageto()
             if self.suggeststhreads():
@@ -447,6 +451,9 @@ class BaseFolder(object):
                   ('syncing flags'          , self.syncmessagesto_flags)]
 
         for (passdesc, action) in passes:
+            # bail out on CTRL-C or SIGTERM
+            if offlineimap.accounts.Account.abort_NOW_signal.is_set():
+                break
             try:
                 action(dstfolder, statusfolder)
             except (KeyboardInterrupt):