help target enhancements

Change target e.g. 'help-linux' to 'linux-help'; consistent with
'linux-clean'

Add '<package>-clean' help description
Fix make <package>[-<distro>[-<arch>]] targets
Makefile:  add util-%.chroot-update target

Update chroots
Update pkg release

- Pick up changes in submodule
- Hopefully work around jessie chroot update not working
RTAI package:  Add clean target
Linux package:  decouple ABI name and pkg version

This allows updates to kernel packages where ABI isn't broken
Change release from 'mk' to 'da'

Package origin is Dovetail Automata, not Machinekit
Update submodules for RTAI packages

RTAI package:
- Patch RTAI for multiple configs on a single system
  - https://github.com/ShabbyX/RTAI/issues/16
- Patch RTAI to fix SSE instructions
- Enable FPU in configuration
- update package from python-support to dh_python2
- bump pkg release
- .gitignore build artifacts

Kernel package:
- Rename RTAI featureset from 'rtai' to 'rtai.x86'
- Remove 'mk' from abiname
- Add hook for featuresets that install headers
  - Use it to update the rtai-config-<kver> script
- Fix module install hook
WIP:  IgH EtherCAT packaging

This isn't properly worked into the autobuilder yet.
Updates to RTAI submodule

- RTAI grub config for isolcpus=
- Add RTDM option
- Add CONFIG_RTAI_CPUS="8" to .config
Updates to linux submodule; bump pkg release to `-5da`

- Add `Provides: linux-image-<xenomai|rtai>` to pkgs
- Remove `Provides: linux-image-<featureset>` hard-coded hack
- Add `Provides: rtai-modules-...` to RTAI kernel package
  - For compatibility with LinuxCNC project kernel pkgs
- Allow templating package relations
  - e.g. `Provides: rtai-modules-%(abiname)s-rtai.x86-%(flavour)s`
- New `bin/gencontrol.py --dump-config` command line argument
  - Handy for debugging
RTAI package config:  disable build on ARM
Makefile:  support packages with no tarballs

The linux-latest package is a `/debian/` directory only.
Add `linux-latest` package

The `linux-latest` package provides a way to drag in kernel packages
without needing to specify the ABI name, which is embedded in the
kernel packages' names.

The `git/linux-latest-deb` submodule was cloned from the upstream
Debian package and modified for these kernels.

A `-p PACKAGE` argument is added to
`pbuild/linux-unpacked-chroot-script.sh` so that it can be used for
more than just the `linux` package, since the `linux-latest` source
package configuration depends on the `linux-support` package.

The `linux-support` package build, previously disabled, is re-added.