Bash automatically resets euid to uid when it executes. This means that the
effective user id of a program at the point it calls febootstrap-supermin-helper
will be lost if any part of execution chain involved bash. This in turn can
result in:

* the generation of an incorrect checksum, which contains the uid.
* the generation of supermin files with a mixture of owners

The -u and -g options allow the caller to pass in an explicit user and group to
run as. febootstrap-supermin-helper will set(u|g)id as appropriate.

If usage information is displayed because of an error, it should go to stderr.
If it is displayed because the -h option was given it should go to stdout.

(Thanks also to Jim Meyering for resolving the git submodule problems).

Recent state of the elf-default-arch script and the hardcoded i386 arch doesn't
allow building on other arches than ix86 or x86_64. See attachment for a fix.
Can be easily extended to support additional secondary arches by adding new
patterns to the elf-default-arch script

Previously in febootstrap-supermin-helper we would visit the
files in supermin.d in arbitrary (ie. readdir) order.  This has
caused a series of heisenbugs where some implicit dependency
between these files has not been honoured.  The latest one is
that '/etc/localtime' can be added to the appliance before '/etc'
has been created (and this operation fails).

Instead of continuing to chase these, this commit forces us to
visit the files in filename order by sorting them before visiting
them.

Note that in libguestfs, the current order is sufficient, because
the files are called:

base.img
daemon.img
hostfiles