JobQueue: fixed incorrect requeuing.

* A dependent job was requeued even if it wasn't part of the queue
before. The code relied on dependent jobs being already enqueued;
but that cannot be guaranteed.
* If a job failed, its dependent jobs are now also set to failed, so
that they won't be requeued at a later point.
* This caused some of the "Launching xxx failed: Operation not allowed"
messages in the boot process. Those actually weren't harmless, and
could mess up the natural job order.

Moved BJob, and JobQueue into the support kit.

* Put it in the BSupportKit namespace, following the style introduced
with the package kit for now.
* The BSupportKit::BJob class no longer knows about the package kit's
Context class. However, the BPackageKit::BJob class does.
* Due to the namespace juggling, a lot of files had to be touched.
* The JobQueue class remains private.
* Due to the way Haiku is built on itself, you cannot build this change
under Haiku with an older release.

Moved BJob, and JobQueue into the support kit.

* Put it in the BSupportKit namespace, following the style introduced
with the package kit for now.
* The BSupportKit::BJob class no longer knows about the package kit's
Context class. However, the BPackageKit::BJob class does.
* Due to the namespace juggling, a lot of files had to be touched.
* The JobQueue class remains private.
* Due to the way Haiku is built on itself, you cannot build this change
under Haiku with an older release.