image creation improvements

Hi,

This patchset contains various improvements for the image creation functionality made by Patchick Ohly during his work on bug #9076:
- fixed dependency calculation for conversion chaining
- renamed COMPRESSION variables to CONVERSION as the term "compression" is no longer accurate
- prioritized specialized image creation methods over using conversion chaining
- support converting masked types

The changes look reasonable to me. However, it would be good to hear other people opinions as some changes are quite complex.

Changes in v2: rebased on top of master-next
returned image_getdepends back to image_types.bbclass
Changes in v3: rebased on top of recent master
Changes in v4: rebased on top of recent master

The following changes since commit 039f47ad197a9a53109c9f3deadd9c35e62c056d:

uclibc: remove meta-yocto-bsp append (2016-07-26 08:56:32 +0100)

are available in the git repository at:

git://git.yoctoproject.org/poky-contrib ed/oe-core/image-type-9076
http://git.yoctoproject.org/cgit.cgi/poky-contrib/log/?h=ed/oe-core/image-type-9076

Patrick Ohly (4):
image.bbclass: fix dependency calculation when using conversion chaining image creation: support converting masked types image.bbclass: rename COMPRESS(ION) to CONVERSION image.bbclass: prefer specialized image creation methods over chaining

 meta/classes/image-live.bbclass                    |   2 +-
 meta/classes/image-vm.bbclass                      |  33 +----
 meta/classes/image.bbclass                         | 119 +++++++++++-------
 meta/classes/image_types.bbclass                   | 140 ++++++++++++++-------
 meta/classes/image_types_uboot.bbclass             |  18 +--
 meta/conf/documentation.conf                       |   1 -
 .../images/build-appliance-image_15.0.0.bb         |   6 +-
 7 files changed, 181 insertions(+), 138 deletions(-)

2.1.4