As muttrc provides a shortcut 'o' for syncing inbox folders, different mailboxes
may not have the same folder name, we should overridden this command in each
account's muttrc file.
Otherwise, a mailbox which has 'INBOX' as its inbox folder will see this error:
ERROR: Account qq: no folder to sync (folderfilter issue?)
*** Finished account 'qq' in 0:06
ERROR: Exceptions occurred during the run!
ERROR: Account qq: no folder to sync (folderfilter issue?)
This patch fix this problem.