[Dovecot] dovecot and nfs readdir vs readdirplus operations

[Wojciech Puchar]

>
> this is small folders. From my practice  average are 10000-20000 mails. Huge 
> are over 150000.
>
>
did tests with artifically created million mail folder.

except i needed to rise vsize limit of dovecot process in config , and 
except first index creation it works smooth with dovecot taking little CPU 
and (after other programs generated some VM pressure) very little RAM, 
with minimal pagein.

roundcube webmail worked smooth including search, thunderbird was 
extremely slow, imap itself wasn't generating considerable load.