fix #615

ref #477

ref #472

http://redmine.alpinelinux.org/issues/480

This is so we don't break 'lbu package -'

lbu did bad things with your /dev/null

this works around an issue when lbu wrongly assumes /media/usb is
mounted when /media/usbdisk is.

ref #91

scripts in /etc/lbu/pre-package.d/ will be executed prior creating the
tar ball and scripts in /etc/lbu/post-package.d/ will be executed after.

if pre-scripts fails, then will package not be created.

ref #220

try avoid ending up with a lbu media without any apkovl.

fixes http://redmine.alpinelinux.org/issues/show/94

fix bug when there are no backups

trap signals and cleanup.
initial lbu revert.

dont override with default encryption if ENCRYPTION is set in lbu.conf. fixed typo in help text. Thanks to Alexander Poslavsky