Don't adjust other cursors when we added a node on the right.

ITS#8258, ITS#7829 fixes checked parent index to see if we were moving
from a left neighbor. Should have just checked to see if current index
was 0, meaning we added on the left. (Parent index may not tell us
anything meaningful after a nested rebalance.)

Parent mc_ki wasn't adjusted if new_indx was > split point

The parent's mc_ki has changed. We need to fix that up as well
in other cursors.

No effect on current code.

...early enough that txn state is left unchanged.

Move the check to the end of txn startup.  Catches env
breakage which happens while the new txn waits for a lock.

* Add MDB_TXN_FINISHED, MDB_TXN_HAS_CHILD, MDB_TXN_BLOCKED.
* Clear mt_numdbs in writers, for TXN_DBI_EXIST() to catch.
  We already do in readers.

Side effects:
* Clean txn up a bit even before freeing it.
* Tweak DEBUG output at txn end. Add DEBUG after commit(writer).

MDB_DBI_CHANGED(,MAIN_DBI) is never true.

mt_env is always set.
Commit(mt_child) resets mt_child, so parent need not.

So far just to help aligning mdb.master and mdb.RE.
We'll make it an option later.

Leonid Yuriev authored Jul 03, 2015 and Hallvard Furuseth committed Oct 25, 2015

The rest of 9a80a8a8
plus commit a937740a.

mdb_xcursor_init1(): md_pad is only used when MDB_DUPFIXED.
mdb_page_split():    Copy mp_pad too. Used by mdb_page_list().

More fallout from 4d02c741.

Taken from mdb_txn_begin(,,MDB_NOMETASYNC, MDB_NOSYNC,,)
without adding those two flags yet, to align with mdb.master:
Part of 54516639 (Renumber...)
+ 8adee946 (Fix per-txn...).

Leonid Yuriev authored Jan 17, 2015 and Hallvard Furuseth committed Oct 25, 2015

commit 9a8eb956 (mdb_txn_renew0)
plus b2ab9910 (reader allocation)
from mdb.master.

David Barbour authored Jan 12, 2015 and Hallvard Furuseth committed Oct 25, 2015

commit b660491d (mdb_txn_id())
plus c36c167c (fix prev commit)
from mdb.master.