As implemented according to issue #1938 for maven builds, it should be possible
to block up-/downstream project in matrix builds too.

As a description, my problem:

We have matrix projects a b c and d. They build a dependency chain a-b-c-d.
At the time, if the projects changes the builds will start parallel and b,c and
d don't have the proper results of the upstream projects and fail.
If a is ready, b is scheduled and so on, the builds all are started again.

On the other side, if d is running and a changes a have to wait until d (or b or
c) is ready. At the time it will be started in parallel and probably the other
projects fail while loosing its dependencies.

Proposal:

Matrix builds should have a flag to be able to block the execution of a project
if an other project in the up-/downstream chain is running.

If the blocking project has finished, the Queue should be reordered according to
the up-/downstream chain and the projects should be build according to its
dependencies. (already queued projects should wait until they are triggered from
upstream project, or deleted from queue as they are started by the upstream
project again)

The parallel build of the axes should not be blocked.

BTW, this is NOT a duplicate of issue #1938, because matrix projects don't
support the blocking, like maven projects do, in using hudson version 1.335