This makes it possible to build an image against a first distribution
(--distribution-chroot) and have the resulting image point to another
distribution (--distribution-binary). We can use this to build against a
snapshot and have the result use the original distribution that was
snapshotted.
Closes: #888507
Note: OLDIFS use makes IFS to be reset to "" instead to it being unset.
Either we need to detect if old IFS was unset to unset it
or we need a proper way of setting it as a local variable.
Even more IFS it's not currently used in
Check_package (which it's called from: binary_hdd).
we should have a clean way of resetting/unsetting IFS when calling Check_package.
The other approach it's to explicitly define IFS with its default value in the
places inside live-build code where we implicitly suppose that it's going to have
its default value.
Previously, we needed to keep the lb_* prefix as the scripts
could also be executed standalone. Since the lb wrapper is
mandatory since squeeze, we can drop this now.