* Add global HAIKU_PACKAGES_UPDATE_ONLY build system variable, which is
set for the "update" and "update-all" build profile actions.
* Change the HAIKU_INCLUDE_IN_CONTAINER_VAR variable on packages to
HAIKU_INCLUDE_IN_PACKAGES for all packages. The variable is also
set for the "update" and "update-all" build profile actions.
* Introduce HAIKU_CONTAINER_INHERIT_UPDATE_VARIABLE on container
variable. If set, the contained variable will be set on the container
when one or more files in it are updated. It is set on packages so an
update of a file in a package causes the package to be updated in the
image.
* Introduce HAIKU_CONTAINER_ALWAYS_CREATE_DIRECTORIES on container
variable. If set, directories will be created also in update mode. It
is set on packages.
* Create rules (build/jam/PackageRules) and a script,
build_haiku_package, to build hpkg files.
* Move all rule invocations that copy files and created symlinks and
directories in the "system" directory from HaikuImage to
HaikuPackages, which creates a package "haiku.hpkg".
* build_haiku_image: Comment out adding the copyrights info to
AboutSystem for the moment.
