Rework undocumented listjoin to create UID sequences

This function was badly named and completely undocumented. Rework it to
avoid copying the full UID list using an iterator. Make it possible to
hand it a list of UIDs as strings rather than implicitely relying on the
fact that they are numeric already. Document the code.

The behavior off the function itself remained otherwise unchanged.

Signed-off-by: Sebastian Spaeth <Sebastian@SSpaeth.de>
Signed-off-by: Nicolas Sebrecht <nicolas.s-dev@laposte.net>

offlineimap/folder/Gmail.py

@@ -55,7 +55,7 @@ class GmailFolder(IMAPFolder):
             try:
                 imapobj.select(self.getfullname())
                 result = imapobj.uid('copy',
-                                     imaputil.listjoin(uidlist),
+                                     imaputil.uid_sequence(uidlist),
                                      self.trash_folder)
                 assert result[0] == 'OK', \
                        "Bad IMAPlib result: %s" % result[0]

offlineimap/folder/IMAP.py

@@ -626,7 +626,7 @@ class IMAPFolder(BaseFolder):
                 self.ui.flagstoreadonly(self, uidlist, flags)
                 return
             r = imapobj.uid('store',
-                            imaputil.listjoin(uidlist),
+                            imaputil.uid_sequence(uidlist),
                             operation + 'FLAGS',
                             imaputil.flagsmaildir2imap(flags))
             assert r[0] == 'OK', 'Error with store: ' + '. '.join(r[1])