[imp] attachment icon

[Andrea Zagli]

i didn't see an attachment icon next to mails in mailbox view

so i searched on google but i found nothing (except very old mails  
from Jan that referring to a parameter in the configuration that now  
seems no longer exist)

but i found on hooks.php that there is a sample function that do this

the question: why is it an optional feature? can i activate it without  
big performances problems?