- Update to version 4.2.0
* Add the arena..reset mallctl, which makes it possible to
discard all of an arena's allocations in a single operation.
* Add the stats.retained and stats.arenas..retained statistics.
* Add the --with-version configure option.
* Support --with-lg-page values larger than actual page size.
* Use pairing heaps rather than red-black trees for various hot
data structures.
* Streamline fast paths of rtree operations.
* Optimize the fast paths of calloc() and [m,d,sd]allocx().
* Decommit unused virtual memory if the OS does not overcommit.
* Specify MAP_NORESERVE on Linux if [heuristic] overcommit is active,
in order to avoid unfortunate interactions during fork(2).
* Fix chunk accounting related to triggering gdump profiles.
* Link against librt for clock_gettime(2) if glibc < 2.17.
* Scale leak report summary according to sampling probability.