Address "should check that we're building on debian through e.g. a 'derivative-is-based-on' variable or somesuch" fixme.

Somewhat fixing sysvinit and casper legacy support, slightly improved patch from Rui Miguel P. Bernardo <rui.bernardo.pt@gmail.com> (Closes: #772522, #772651).

This however will still not work properly building upstart based
images but they have been broken/unsupported anyway since a long
time.

With linux 3.16 in Debian Jessie, armmp and armmp-lpae are the
only armhf flavours availale. On armel, we lost the support of
the iop32x flavour.

extlinux configuration for the bootable image is installed to
/boot/extlinux, matching the extlinux-install script in Debian.

From the configuration point of view it's still called "syslinux",
the same as the rest of the syslinux family (pxelinux, isolinux etc.)

This might come back in future if there's demand for it
and the base is sufficiently cleaned up first.

Adding hook to disable 70-persistent-cd.rules udev rule to prevent udev remember the cd device name both the one of the build system and the one of the live system (Closes: #706926).

Renaming remove-udev-persistent-rules.chroot hook to remove-udev-persistent-net-rules.chroot for future additional udev hooks.

If LB_HDD_SIZE is "auto" the size will be determined automatically as before
else it will be the given size in MB.

Also setting the default for this to "auto"

[A-Z] and [a-z] expands if there is a file or directory with one letter in the
directory.

Dropping dedicated backports mirror handling, not needed anymore with the move of backports.d.o into ftp.d.o.

Adding check for ntfs-3g on the host system, precluding the initial ntfs binary filesystem support (Closes: #697793).

This is 'debranding' in the sense that live-build defaults are for people
building images with a config from scratch, live-build should not
have the options that we use for the official prebuilt debian-live
images as debian-defaults for all images and force that upon everyone
(as defaults). Rather, a 'lb config' should produce a as vanilla as
possible configuration tree.

Dropping powerpc bootloader support (yaboot), there is nobody actively maintaining this in live-build.

Dropping theme package support, themes are either in the config tree or the embedded one from live-build is used.