(ITS#7620) LMDB overflow page management

Full_Name: Howard Chu Version: 2.4.35 OS: URL: ftp://ftp.openldap.org/incoming/ Submission from: (NULL) (78.155.233.73) Submitted by: hyc

Pages that are dirtied get pulled out of the freeDB. If they are freed in the same txn they should be returned to their original place in the freeDB instead of joining the current txn's list of freed pages. This is particularly important for overflow pages because otherwise we can consume a lot of overflow pages rapidly in some cases.

Commit e7f6767ea815fe0ada1f95037dfdec176ec4d5bb in mdb.master is for this issue, but it needs additional fixes.