distributed pushed down joins - node-failure handling done

node-failure handling was as expected lots of small changes to various pieces of the code.
some non compatible protocol changes performed (nice not to have any existing GA release to care about :)

also when doing this, I re-implemented entire "abort of join"-handling.
it should now also be capable of handling aborting more complex joins
(but node-failure is still an special case)

this means that "testSpj -n NF_Join" now passes!!

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this is an important step towards a releasable version.

note: this has only been implemented in the branch which also contains extension for scan.vs.scan joins. I.e not in the branch released as preview.

and, OleJohn integrated support for filters on child-joins with mysqld.

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And as always please provide feedback on preview release that we made!