Merge lp://qastaging/~jelmer/launchpad/buildrecipe-allow-fallback-to-native into lp://qastaging/launchpad

[r=bac][bug=885497] Pass --allow-fallback-to-native to "bzr dailydeb".

Pass --allow-fallback-to-native to "bzr dailydeb".

At the moment, Launchpad runs a version of bzr-builder that converts *all*
non-native source packages to native packages.

Newer versions of bzr-builder support properly building non-native packages too,
and by default no longer convert non-native packages to native packages.
Instead, bzr-builder actually attempts to build a propery native package.

Since building a native package requires an orig tarball, most of the
existing builds on Launchpad can't actually be built as a non-native package.
And because they're daily builds, it makes more sense to build them as
a native package too. The reason some try to build a non-native is
because they inherit their packaging data from Debian or Ubuntu packages.

Passing --allow-fallback-to-native makes bzr dailydeb keep the old
behaviour of converting non-native packages to native packages,
but only if no upstream tarball was found.

This will need to be deployed together with the new version of bzr-builder,
which is already available in the cat archive,
as old versions don't have the --allow-fallback-to-native option.