[Dovecot] config typo in 2.0.alpha2

[Mike Abbott]

The mdbox_rotate_size and mdbox_rotate_min_size parameters are  
specified in bytes not kilobytes.

doc/example-config/conf.d/mail.conf:
# Maximum dbox file size in kilobytes until it's rotated.
#mdbox_rotate_size = 2048

# Minimum dbox file size in kilobytes before it's rotated
# (overrides mdbox_rotate_days)
#mdbox_rotate_min_size = 16

src/lib-storage/index/dbox-multi/mdbox-settings.c:
	MEMBER(mdbox_rotate_size) 2048*1024,
	MEMBER(mdbox_rotate_min_size) 16*1024,