update jemalloc

This includes optimizations to the thread cache and support for
shrinking and expanding huge (>4M) allocations in-place.

diff --git a/src/jemalloc b/src/jemalloc
index 2dba541881fb8e35246d653bbe2e7c7088777a4a..b001609960ca33047e5cbc5a231c1e24b6041d4b 160000 (submodule)
--- a/src/jemalloc
+++ b/src/jemalloc
@@ -1 +1 @@
-Subproject commit 2dba541881fb8e35246d653bbe2e7c7088777a4a
+Subproject commit b001609960ca33047e5cbc5a231c1e24b6041d4b