Refuse to process mailboxes owned by someone else

This should also protect people relying on the old setuid feature.
If the mailbox is local, by checking the ownership we necessarily check for
existance.

archivemail.py

@@ -1100,6 +1100,17 @@ def archive(mailbox_name):
     if not dest_dir:
         dest_dir = os.getcwd()
     check_sane_destdir(dest_dir)
+    is_imap = urlparse.urlparse(mailbox_name)[0] in ('imap', 'imaps')
+    if not is_imap:
+        # Check if the mailbox exists, and refuse to mess with other people's
+        # stuff
+        try:
+            fuid = os.stat(mailbox_name).st_uid
+        except OSError, e:
+            user_error(str(e))
+        else:
+            if fuid != os.getuid():
+                user_error("'%s' is owned by someone else!" % mailbox_name)
 
     vprint("archiving '%s' to '%s' ..." % (mailbox_name, final_archive_name))
     old_temp_dir = tempfile.tempdir
@@ -1112,7 +1123,6 @@ def archive(mailbox_name):
         tempfile.tempdir = new_temp_dir
         vprint("set tempfile directory to '%s'" % new_temp_dir)
 
-        is_imap = urlparse.urlparse(mailbox_name)[0] in ('imap', 'imaps')
         if is_imap:
             vprint("guessing mailbox is of type: imap(s)")
             _archive_imap(mailbox_name, final_archive_name)
@@ -1129,7 +1139,7 @@ def archive(mailbox_name):
                 vprint("guessing mailbox is of type: MH")
                 _archive_dir(mailbox_name, final_archive_name, "mh")
         else:
-            user_error("'%s': no such file or directory" % mailbox_name)
+            user_error("'%s' is not a normal file or directory" % mailbox_name)
 
         # remove our special temp directory - hopefully empty
         os.rmdir(new_temp_dir)